U.S. patent application number 12/899201 was filed with the patent office on 2011-04-07 for method and apparatus for determining radiation.
This patent application is currently assigned to Massachusetts Institute of Technology. Invention is credited to Jose M. Lobez, Timothy M. Swager.
Application Number | 20110081724 12/899201 |
Document ID | / |
Family ID | 43823473 |
Filed Date | 2011-04-07 |
United States Patent
Application |
20110081724 |
Kind Code |
A1 |
Swager; Timothy M. ; et
al. |
April 7, 2011 |
METHOD AND APPARATUS FOR DETERMINING RADIATION
Abstract
The present invention relates to devices, systems, and methods
for determination of ionizing radiation. In some embodiments, the
devices comprise nanocomposite materials containing nanostructures
(e.g., carbon nanotubes) dispersed in radiation sensitive polymers.
In some cases, the device may include a conductive pathway that may
be affected upon exposure to ionizing radiation. Embodiments
described herein may provide inexpensive, large area, low power,
and highly sensitive radiation detection materials/devices.
Inventors: |
Swager; Timothy M.; (Newton,
MA) ; Lobez; Jose M.; (Boston, MA) |
Assignee: |
Massachusetts Institute of
Technology
Cambridge
MA
|
Family ID: |
43823473 |
Appl. No.: |
12/899201 |
Filed: |
October 6, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61249042 |
Oct 6, 2009 |
|
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Current U.S.
Class: |
436/57 ; 204/400;
205/775; 422/68.1; 977/742; 977/762; 977/773 |
Current CPC
Class: |
B82Y 15/00 20130101;
G01T 1/04 20130101 |
Class at
Publication: |
436/57 ;
422/68.1; 204/400; 205/775; 977/742; 977/762; 977/773 |
International
Class: |
G01N 23/00 20060101
G01N023/00; G01N 27/26 20060101 G01N027/26 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] This invention was made with the support under the following
government contract: DMR0706408 awarded by the National Science
Foundation. The government has certain rights in the invention.
Claims
1. A device for determining ionizing radiation, comprising: a
sensor material comprising a polymer material, wherein at least a
portion of the polymer material undergoes a change in a
polymerization characteristic upon exposure of the device to
ionizing radiation; and a signal generator that generates a signal
responsive to a change in polymerization characteristic, indicative
of ionizing radiation.
2. A device for determining ionizing radiation, comprising: a
sensor material comprising a plurality of nanostructures positioned
relative to each other so as to together define an average distance
between adjacent nanostructures, wherein the average distance
between adjacent nanostructures is altered upon exposure of the
device to ionizing radiation; and a signal generator that generates
a signal responsive to a change in the average distance between
adjacent nanostructures, indicative of ionizing radiation.
3. A device as in claim 1, wherein the sensor material comprises a
plurality of nanostructures and a polymer material integrally
connected to at least a portion of the plurality of
nanostructures.
4. A device as in claim 1, further comprising a first electrode and
a second electrode, wherein the sensor material is in
electrochemical communication with the first and the second
electrodes and resistance to current flow between the first and
second electrode is affected by the sensor material.
5. A device as in claim 1, wherein the change in polymerization
characteristic comprises depolymerization of at least a portion of
the polymer material.
6. A device as in claim 1, wherein the polymer material comprises a
poly(olefin sulfone), optionally substituted.
7. A device as in claim 1, wherein the polymer material comprises a
polyaldehyde, optionally substituted.
8. A device as in claim 1, wherein the sensor material further
comprises a species that interacts with the nanostructures via
pi-pi stacking interactions.
9. A device as in claim 1, wherein the sensor material comprises
polycyclic aromatic hydrocarbons.
10. A device as in claim 1, wherein the sensor material comprises
pyrene groups.
11. A device as in claim 1, wherein the sensor material comprises a
group that increases the cross-section value of the sensor material
for interaction with ionizing radiation.
12. A device as in claim 1, wherein the sensor material comprises a
metal-containing group.
13. A device as in claim 12, wherein the metal-containing group is
a metal complex or a metal nanoparticle.
14. A device as in claim 12, wherein the metal-containing group
comprises a heavy metal.
15. A device as in claim 12, wherein the metal-containing group
comprises bismuth.
16. A device as in claim 12, wherein the metal-containing group
comprises gadolinium.
17. A device as in claim 1, wherein the sensor material comprises a
plurality of metal-containing groups, each group having a different
cross-section value for interaction with ionizing radiation.
18. A device as in claim 1, wherein the sensor material comprises a
polymer having the structure, ##STR00021## wherein: R and R' can be
the same or different and are alkyl, heteroalkyl, alkenyl,
heteroalkenyl, alkynyl, heteroalkynyl, aryl, heteroaryl, any of
which may be substituted; and n is 1 or greater.
19. A device as in claim 18, wherein n is 10 or greater.
20. A device as in claim 18, wherein R is alkyl, optionally
substituted with an azide group or a polycyclic aromatic
hydrocarbon.
21. A device as in claim 1, wherein the sensor material comprises a
polymer having the structure, ##STR00022## wherein: R.sup.1 and
R.sup.2 can be the same or different and are alkyl, heteroalkyl,
alkenyl, heteroalkenyl, alkynyl, heteroalkynyl, aryl, heteroaryl,
any of which may be substituted; m, n, and can be 0 or greater,
provided that at least one of m, n, and o is 1 or greater; and x is
1 or greater.
22. A device as in claim 21, wherein x is 3 or greater.
23. A device as in claim 1, wherein the sensor material comprises a
polymer having the structure, ##STR00023## wherein R and R' can be
the same or different and are alkyl, heteroalkyl, alkenyl,
heteroalkenyl, alkynyl, heteroalkynyl, aryl, heteroaryl, any of
which may be substituted; a, b, c, and d are 0 or greater; and m
and n can be 0 or greater, provided that at least one of m and n is
1 or greater; and x is 1 or greater.
24. A device as in claim 1, wherein the sensor material comprises a
polymer having the structure, ##STR00024##
25. A device as in claim 1, wherein the sensor material comprises a
polymer having the structure, ##STR00025## wherein R, R', and R''
can be the same or different and can be alkyl, heteroalkyl,
alkenyl, heteroalkenyl, alkynyl, heteroalkynyl, aryl, heteroaryl,
any of which may be substituted; a, b, c, d, and e are 0 or
greater; and m, n, and o can be 0 or greater, provided that at
least one of m, n, and o is 1 or greater; and x is 1 or
greater.
26. A device as in claim 1, wherein the sensor material comprises a
mixture of polymers.
27. A device as in claim 3, wherein the nanostructures are
nanotubes, nanorods, nanoribbons, nanowires, or nanoparticles.
28. A device as in claim 3, wherein the nanostructures are
single-walled carbon nanotubes or multi-walled carbon
nanotubes.
29. A device as in claim 3, wherein the nanostructures are gold,
silver, copper, bismuth, or gadolinium nanowires.
30. A system, comprising a plurality of devices as described in
claim 1.
31. A method for determining ionizing radiation, comprising:
exposing a device comprising a sensor material comprising a polymer
material to an environment suspected of containing ionizing
radiation, wherein the ionizing radiation, if present, interacts
with the polymer material such that at least a portion of the
polymer material undergoes a change in a polymerization
characteristic, thereby generating a determinable signal; and
determining the signal.
32. A method as in claim 31, wherein the sensor material further
comprises a plurality of nanostructures, and the polymer material
is integrally connected to at least a portion of the plurality of
nanostructures.
33. A method for determining ionizing radiation, comprising:
exposing a device comprising a plurality of nanostructures
positioned relative to each other at a distance so as to together
define an average distance between adjacent nanostructures, to an
environment suspected of containing ionizing radiation, wherein the
ionizing radiation, if present, interacts with at least a portion
of the device to alter the average distance between adjacent
nanostructures, thereby generating a determinable signal; and
determining the signal.
34. A method as in claim 33, further comprising a polymer material
integrally connected to at least a portion of the plurality of
nanostructures.
35. A method as in claim 31, wherein at least a portion of the
polymer material undergoes depolymerization upon exposure to
ionizing radiation.
36. A method as in claim 31, wherein the device further comprises a
first electrode and a second electrode in electrochemical
communication with the sensor material, such that the determinable
signal comprises a change in resistance to current flow between the
first and second electrodes.
37. A method as in claim 31, wherein the device further comprises a
first electrode and a second electrode in electrochemical
communication with the sensor material, such that the determinable
signal comprises a change in capacitance to current flow between
the first and second electrodes.
38. A method as in claim 36, wherein the resistance to current flow
between the first and second electrodes decreases upon exposure to
ionizing radiation, thereby generating the determinable signal.
39. A method as in claim 33, wherein the average distance between
adjacent nanostructures decreases upon exposure to ionizing
radiation, thereby generating the determinable signal.
40. A method as in claim 31, wherein the determinable signal
comprises a change in fluorescence emission.
41. A method as in claim 31, wherein the determinable signal
comprises a colorimetric change.
42. A method as in claim 31, wherein the polymer material comprises
a poly(olefin sulfone), optionally substituted, such that exposure
to ionizing radiation results in depolymerization of a poly(olefin
sulfone) to produce sulfur dioxide and an olefin species.
43. A method as in claim 31, wherein the polymer material comprises
a polyaldehyde, optionally substituted, such that exposure to
ionizing radiation results in depolymerization of a polyaldehyde to
produce aldehyde species.
44. A method as in claim 31, wherein the sensor material further
comprises a species that interacts with the nanostructures via
pi-pi stacking interactions.
45. A method as in claim 31, wherein the sensor material comprises
polycyclic aromatic hydrocarbons.
46. A method as in claim 31, wherein the sensor material comprises
pyrene groups.
47. A method as in claim 31, wherein the sensor material comprises
a group that increases the opacity of the sensor material to
ionizing radiation.
48. A method as in claim 31, wherein the sensor material comprises
a metal-containing group.
49. A method as in claim 48, wherein the metal-containing group is
a metal complex or a metal nanoparticle.
50. A method as in claim 48, wherein the metal-containing group
comprises a heavy metal.
51. A method as in claim 48, wherein the metal-containing group
comprises bismuth.
52. A method as in claim 48, wherein the metal-containing group
comprises gadolinium.
53. A method as in claim 31, wherein the sensor material comprises
a plurality of metal-containing groups, each group having a
different cross-section value for interaction with ionizing
radiation.
54. A method as in claim 31, wherein the sensor material comprises
a polymer having the structure, ##STR00026## wherein: R and R' can
be the same or different and are alkyl, heteroalkyl, alkenyl,
heteroalkenyl, alkynyl, heteroalkynyl, aryl, heteroaryl, any of
which may be substituted; and n is 1 or greater.
55. A method as in claim 54, wherein n is 10 or greater.
56. A method as in claim 54, wherein R is alkyl, optionally
substituted with an azide group or a polycyclic aromatic
hydrocarbon.
57. A method as in claim 31, wherein the sensor material comprises
a polymer having the structure, ##STR00027## wherein: R.sup.1 and
R.sup.2 can be the same or different and are alkyl, heteroalkyl,
alkenyl, heteroalkenyl, alkynyl, heteroalkynyl, aryl, heteroaryl,
any of which may be substituted; m, n, and can be 0 or greater,
provided that at least one of m, n, and o is 1 or greater; and x is
1 or greater.
58. A method as in claim 57, wherein n is 3 or greater.
59. A method as in claim 31, wherein the sensor material comprises
a polymer having the structure, ##STR00028## wherein R and R' can
be the same or different and are alkyl, heteroalkyl, alkenyl,
heteroalkenyl, alkynyl, heteroalkynyl, aryl, heteroaryl, any of
which may be substituted; a, b, c, and d are 0 or greater; and m
and n can be 0 or greater, provided that at least one of m and n is
1 or greater; and x is 1 or greater.
60. A method as in claim 31, wherein the sensor material comprises
a polymer having the structure, ##STR00029##
61. A method as in claim 31, wherein the sensor material comprises
a polymer having the structure, ##STR00030## wherein R, R', and R''
can be the same or different and can be alkyl, heteroalkyl,
alkenyl, heteroalkenyl, alkynyl, heteroalkynyl, aryl, heteroaryl,
any of which may be substituted; a, b, c, d, and e are 0 or
greater; and m, n, and o can be 0 or greater, provided that at
least one of m, n, and o is 1 or greater; and x is 1 or
greater.
62. A method as in claim 31, wherein the sensor material comprises
a mixture of polymers.
63. A method as in claim 31, wherein the sensor material comprises
a first polymer and a second polymer, such that exposure to
ionizing radiation results in depolymerization of the first polymer
to produce an initiator species, wherein the initiator species
interacts with the second polymer to result in depolymerization of
the second polymer.
64. A method as in claim 31, wherein the sensor material comprises
an additive, such that, upon exposure to ionizing radiation, the
additive interacts with the ionizing radiation to produce an
initiator species which then interacts with the polymeric material
such that at least a portion of the polymer material undergoes
depolymerization.
65. A method as in claim 32, wherein the nanostructures are
nanotubes, nanorods, nanoribbons, nanowires, or nanoparticles.
66. A method as in claim 32, wherein the nanostructures are
single-walled carbon nanotubes or multi-walled carbon
nanotubes.
67. A method as in claim 32, wherein the nanostructures are gold,
silver, copper, bismuth, or gadolinium nanowires.
68. A method as in claim 31, wherein the ionizing radiation
comprises gamma rays, X-rays, ultraviolet rays, neutrons,
electrons, .alpha.-particles, or .beta.-particles.
69. A device as in claim 1, wherein the sensor material comprises a
polymer having the structure, ##STR00031## wherein a, b, w, and n
are each individually 0 or greater, R is alkyl, aryl, heteroalkyl,
heteroaryl, each optionally substituted
70. A method as in claim 31, wherein the sensor material comprises
a polymer having the structure, ##STR00032## wherein a, b, w, and n
are each individually 0 or greater, R is alkyl, aryl, heteroalkyl,
heteroaryl, each optionally substituted.
71. A device as in claim 18, wherein R is alkyl, optionally
substituted with COOR', wherein R' is H, alkyl, aryl, heteroalkyl,
heteroaryl, or a metal-containing species.
72. A device as in claim 71, wherein R' is gadolinium.
73. A method as in claim 54, wherein R is alkyl, optionally
substituted with COOR', wherein R' is H, alkyl, aryl, heteroalkyl,
heteroaryl, or a metal-containing species
74. A method as in claim 73, wherein R' is gadolinium.
75. A device as in claim 69, wherein a, b, and w are each
individually 0 or greater and n is 1 or greater.
76. A method as in claim 70, wherein a, b, and w are each
individually 0 or greater and n is 1 or greater.
Description
FIELD OF THE INVENTION
[0002] The present invention generally relates to devices and
systems for determining ionizing radiation, and related
methods.
BACKGROUND OF THE INVENTION
[0003] Detection and dosimetry of ionizing radiation are crucial in
several fields such as energy, national security, biological and
nuclear research, and in other advanced applications such as
monitoring the attrition of materials in space travel. The most
common systems for the detection and dosimetry of ionizing
radiation usually have one or several of the following drawbacks:
incapability to produce a real-time signal, expensive and/or
complicated manufacturing, need for operation at low temperatures,
low sensitivity to non-charged radiation, or voluminous size.
Although organic materials present the advantages of being easily
processed, synthetic versatility, and relatively low cost,
deployment of organic systems as small size ionizing radiation
detectors and dosimeters has been traditionally limited to the
detection of charged particles, owing to the low cross sections of
elements incorporated in these molecules towards uncharged
radiation. Additionally, many devices for the detection and
dosimetry of ionizing radiation suffer from drawbacks including
inability to produce an in situ signal as is the case with film
badges for dosimetry, expensive and/or complicated manufacturing,
need for operation at low temperatures, low sensitivity to
uncharged radiation, voluminous size like the Geiger counter, or
the size and high voltages associated with .sup.3He or BF.sub.3
proportional tubes.
SUMMARY OF THE INVENTION
[0004] The present invention provides devices for determining
ionizing radiation. In some embodiments, the device comprises a
sensor material comprising a polymer material, wherein at least a
portion of the polymer material undergoes a change in a
polymerization characteristic upon exposure of the device to
ionizing radiation, and a signal generator that generates a signal
responsive to a change in polymerization characteristic, indicative
of ionizing radiation.
[0005] In some embodiments, the device comprises a sensor material
comprising a plurality of nanostructures positioned relative to
each other so as to together define an average distance between
adjacent nanostructures, wherein the average distance between
adjacent nanostructures is altered upon exposure of the device to
ionizing radiation, and a signal generator that generates a signal
responsive to a change in the average distance between adjacent
nanostructures, indicative of ionizing radiation.
[0006] The present invention also provides various methods for
determining ionizing radiation. In some embodiments, the method
comprises exposing a device comprising a polymer material to an
environment suspected of containing ionizing radiation, wherein the
ionizing radiation, if present, interacts with the polymer material
such that at least a portion of the polymer material undergoes a
change in a polymerization characteristic, thereby generating a
determinable signal, and determining the signal.
[0007] In some embodiments, the method comprises exposing a device
comprising a plurality of nanostructures positioned relative to
each other at a distance so as to together define an average
distance between adjacent nanostructures, to an environment
suspected of containing ionizing radiation, wherein the ionizing
radiation, if present, interacts with at least a portion of the
device to alter the average distance between adjacent
nanostructures, thereby generating a determinable signal, and
determining the signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 shows a device for determination of ionizing
radiation (a) before and (b) after exposure to ionizing radiation,
where the device comprises nanostructures and a polymer
material.
[0009] FIG. 2 shows an example of the synthesis of poly(olefin
sulfone)s.
[0010] FIG. 3 shows an example of the synthesis of azide-containing
poly(olefin sulfone)s.
[0011] FIG. 4A illustrates examples of alkyne-containing species
that may be reacted via "click" chemistry.
[0012] FIG. 4B shows the post-polymerization modification of a
poly(olefin sulfone) with pyrene groups using "click"
chemistry.
[0013] FIG. 4C shows the post-polymerization modification of a
poly(olefin sulfone) with a bismuth-containing group using "click"
chemistry.
[0014] FIG. 5 shows a gadolinium-containing compound that may be
appended to an azide-containing polymer via "click" chemistry.
[0015] FIG. 6 shows atomic force microscopy (AFM) images of a
single-walled carbon nanotube (SWCNT)/polymer thin film, (a) as
cast and (b) after extraction of the polymer more clearly showing
the SWCNT network; (c) an optical image of SWCNT/polymer film
deposited on glass slides; (d) a free-standing SWCNT/polymer film
floating on water surface; and (e) a SWCNT/polymer film transferred
on silicon substrate.
[0016] FIG. 7 shows a poly(olefin sulfone) (POS) incorporating
2-methyl-1-pentene.
[0017] FIG. 8 shows the synthesis of a polyaldehyde (PAL)
containing an endcap.
[0018] FIG. 9 shows a cascade of chemical reactions involving
depolymerization of a poly(olefin sulfone) and a polyaldehyde.
[0019] FIG. 10 shows examples of cationic complexes useful in
chemically amplified lithography.
[0020] FIGS. 11A-C show the syntheses of a polymer-coated bismuth
nanostructures.
[0021] FIG. 12 provides a schematic representation of
interdigitated electrodes.
[0022] FIG. 13 shows a graph of the different components of the
total cross-section of bismuth for gamma-ray interaction.
[0023] FIG. 14 shows a schematic illustration of an array device
and differential responses to different energy ionization
radiation.
[0024] FIG. 15 shows the .sup.10B(n, .alpha.) reaction.
[0025] FIG. 16 shows an example of an ionic liquid.
[0026] FIG. 17 illustrates a schematic representation of a device
for neutron detection.
[0027] FIG. 18 shows a graph of the molar ratio of 6-azido-1-hexene
(X.sub.B) in the feed (x axis) vs. molar ratio of repeat unit
containing azide monomer (X.sub.b), as determined by
.sup.1H-NMR.
[0028] FIG. 19 shows a plot of the increase in conductivity for a
series of POS/MWCNT composites, upon exposure to gamma rays.
[0029] FIG. 20 shows (a) .sup.1H-NMR spectra for POS with different
ratios of Xa, Xb (Xa+Xb=1) and (b) corresponding IR spectra, for
polymer 2.
[0030] FIG. 21 shows IR Spectra of POS with different degrees of
functionalization, including (i) polymer 2, with 44 mol % of
azide-containing repeat unit (X.sub.b=0.44); (ii) polymer 5, with
24 mol % pyrene containing repeat unit, 20 mol % repeat unit
containing azide groups; and (iii) polymer 6, with 24 mol % pyrene
containing repeat unit, 20 mol % bismuth containing repeat
unit.
[0031] FIG. 22 shows images of films containing (A-A1) multi-walled
carbon nanotubes (MWCNTs), (B-B1) polymer 1/MWCNT, and (C-C1)
polymer 5 (24 mol % Pyrene)/MWCNT.
[0032] FIG. 23 shows images of films containing polymer 1/MWCNT
(D-D1) before irradiation and (E-E1) after irradiation with a high
dose of radiation.
[0033] Other aspects, embodiments, and features of the invention
will become apparent from the following detailed description when
considered in conjunction with the accompanying drawings. The
accompanying figures are schematic and are not intended to be drawn
to scale. For purposes of clarity, not every component is labeled
in every figure, nor is every component of each embodiment of the
invention shown where illustration is not necessary to allow those
of ordinary skill in the art to understand the invention. All
patent applications and patents incorporated herein by reference
are incorporated by reference in their entirety. In case of
conflict, the present specification, including definitions, will
control.
DETAILED DESCRIPTION
[0034] The present invention generally provides devices and systems
capable of interacting with ionizing radiation (e.g., gamma rays,
neutrons) to produce an observable signal from the device, and
related methods. In some cases, methods for in situ and/or
real-time detection of ionizing radiation are provided.
[0035] The embodiments described herein may be useful in the
determination, characterization, and/or dosimetry of at least one
type of ionizing radiation. In some cases, the devices may exhibit
high sensitivity to ionizing radiation and may distinguish between
various types of radiation. Some embodiments may also provide
simplified, less bulky sensor devices that may advantageously be
operated at ambient temperature and/or without need for high
voltages associated with .sup.3He or BF.sub.3 proportional tubes.
Devices and methods described herein may provide an inexpensive,
modular sensor platform having applications for energy, national
security, biological and nuclear research, as well as other
advanced applications such as monitoring the attrition of materials
in space.
[0036] In some cases, ionizing radiation may be determined by
monitoring, for example, a change in a signal of a material (e.g.,
sensor material) present within the device, upon exposure to
ionizing radiation. In some cases, the change in signal may be
associated with an interaction between the device and the
radiation, a chemical reaction within the device, or a change in
polymerization state of a component of the device. The signal may
comprise an electrical, optical, or other property of the device,
as described further below. For example, the method may involve use
of a component having a resistance, where the resistance of the
component is affected by (e.g., responsive to) ionizing radiation.
Such as signal can be read-out by a simple, low power and low
current circuit, without need for a bulky apparatus, like in the
case of a Geiger counter. In other embodiment, the capacitance of a
component is affected by ionizing radiation, where the change in
capacitance may be determined without need for a complete circuit.
In other embodiments, the method may involve use of a component
having a luminescence emission (e.g., fluorescence), where a
characteristic of the emission (e.g., wavelength, intensity, etc.)
is affected by ionizing radiation.
[0037] Some embodiments of the invention may also provide devices,
or systems comprising a plurality of devices, for determination of
ionizing radiation and its energy. The device, or portion thereof,
may interact with ionizing radiation such that a chemical event
(e.g., chemical reaction, change in polymerization state) occurs,
giving rise to a determinable signal, or change in signal. In some
cases, a single chemical event within the device may trigger a
cascade of events, which may produce an amplified response to
ionizing radiation. As used herein, "ionizing radiation" is given
its ordinary meaning in the art and refers to nuclei or subatomic
particles or electromagnetic waves having sufficient energy to
ionize an atom or molecule. Various types of ionizing radiation
exist, including ultraviolet rays, X-rays, gamma rays, alpha
particles, beta particles, neutrons, and electrons.
[0038] In some embodiments, the device may include a sensor
material that may be affected by interaction with ionizing
radiation, generating a determinable signal. In some cases, the
device may comprise a sensor material that is responsive to one or
more types of ionizing radiation. The sensor material may comprise
a material that is capable of undergoing a change in one or more
properties upon exposure to ionizing radiation. For example, the
sensor material may include a conductive, semiconductive, or
semimetallic material having electrical properties that may be
affected by the presence of ionizing radiation. In some cases, the
sensor material may include a luminescent material having optical
properties that may be affected by the presence of an ionizing
radiation. In some embodiments, the sensor material may include a
material capable of undergoing a volumetric or dimensional change
upon exposure to ionizing radiation. The devices described herein
may be designed and fabricated to determine one or more types of
ionizing radiation. In some embodiments, the device is designed and
fabricated to determine gamma rays, neutrons, other types of
radiation, or a combination thereof.
[0039] In some embodiments, the sensor material may comprise a
conductive, semiconductive, semimetallic species, or other species
capable of transporting charge to create a conductive pathway. The
conductive, semiconductive, or semimetallic species may include
inorganic materials (e.g., metals, alloys, semiconductors), organic
materials (e.g., polymer materials), organometallic materials,
and/or combinations thereof. In some cases, the sensor material may
include a plurality of nanostructures (e.g., nanotubes, nanowires,
nanoribbons, nanoparticles, etc.). The nanostructures may be
selected to exhibit, for example, high charge mobilities and/or
resistance to damage from ionizing radiation. In some cases,
mixtures or assemblies of nanostructures may be utilized. Some
embodiments may involve the use of carbon nanotubes, such as
single-walled carbon nanotubes (SWCNTs) and/or multi-walled carbon
nanotubes (MWCNTs), which can display relatively high charge
mobilities (e.g., 100,000 cm.sup.2/Vs for SWCNTs). In some cases,
nanowires, such as gold, silver, copper, bismuth, gadolinium
nanowires, may be used as the conductive species. In some cases,
the conductive, semiconductive, or semimetallic species may
comprise nanoparticles (e.g., gold nanoparticles).
[0040] In some embodiments, the nanostructures are positioned
relative to one another in the device at a distance, so as to
together define an average distance between adjacent
nanostructures. In operation, ionizing radiation may affect the
sensor material such that the average distance between adjacent
nanostructures is altered (e.g., increased, decreased), indicating
the presence and/or amount of ionizing radiation. For example, the
distance between adjacent nanostructures may decrease, such that
the nanostructures that have high charge mobility and/or high
radiation damage threshold aggregate to form a circuit. Such
changes in the electrochemical state of the nanostructures may be
used to indicate the presence of ionizing radiation.
[0041] Changes in the relative position of nanostructures in the
device may be achieved by, for example, arranging the
nanostructures in combination with (e.g., dispersed within) a
matrix responsive to ionizing radiation. For example, the sensor
material may comprise a polymer material, wherein at least a
portion of the polymer material may undergo a change in a
polymerization characteristic upon exposure of the device to
ionizing radiation. The change in polymerization characteristic may
be, for example, a change in the degree of polymerization (e.g.,
increased polymerization, depolymerization, etc.), morphology,
chemical structure, or other property of the polymer material. In
some cases, the ionizing radiation may interact with the polymer
material such that a portion of the polymer undergoes degradation
or depolymerization. As used herein, the term "depolymerization" is
given its ordinary meaning in the art and refers to a process by
which a macromolecule (e.g., a polymer) is converted (e.g.,
decomposed, cleaved) into smaller compounds by cleavage of at least
one bond of the macromolecule. For example, a polymeric species may
be depolymerized into its monomeric constituents via cleavage of
one or more bonds of the polymer backbone. In some embodiments,
chain scission caused by gamma rays, neutrons, or other forms of
radiation can result in disassembly of polymer chains.
[0042] Some embodiments may involve the use of a polymer material
that, upon exposure to ionizing radiation, generates at least one
initiator species capable of causing a change in a polymerization
characteristic of at least a portion of the sensor material. For
example, depolymerization of a first polymer may generate a
plurality of initiator species capable of effecting
depolymerization of a second polymer, thereby producing an
amplified response from the device. The first and second polymers
may be the same type of polymer species or may be different
polymers species (e.g., may have different chemical
structures).
[0043] In one set of embodiments, the sensor material comprises
carbon nanotubes and a polymer material integrally connected to at
least a portion of the plurality of carbon nanotubes. The term
"integrally connected," when referring to two or more objects,
means objects that do not become separated from each other during
the course of normal use, i.e., separation of the objects generally
requires at least the use of tools, and/or by causing damage to at
least one of the components, for example, by breaking, peeling,
dissolving, etc. In some cases, the carbon nanotubes are dispersed
within the polymer material, such that individual nanotubes have
minimal or substantially no physical contact with adjacent
nanotubes.
[0044] The device may further comprise a first electrode and a
second electrode arranged in electrochemical communication with the
sensor material, where current flow between the electrodes is
affected by the sensor material. FIG. 1A shows an illustrative
embodiment of a device, prior to exposure to ionizing radiation,
where nanostructure 10 is insulated from an adjacent nanostructure
by polymer material 20. That is, the nanostructures are dispersed
within the polymer material, preventing optimal contact between the
nanostructures and resulting in high resistance and low
conductivity (e.g., no signal). The polymer material maintaining
the nanojunctions between nanostructures serves as an insulating
matrix that is thermally stable, but depolymerizes rapidly with a
radiation induced chain scission event, thus placing the
nanostructures at the cusp of a percolative threshold to forming a
circuit between the two electrodes. Upon exposure to radiation, as
shown in FIG. 1B, at least a portion of polymer material 20 may
undergo depolymerization, resulting in aggregation of the
nanostructures and producing a conductive network with decreased
resistance and increased conductivity (e.g., signal generation).
The increase in conductivity may be detected by amperometry
(measurement over time of the current intensity, I, between two
electrodes at a constant potential, V), or other methods.
[0045] The sensor material may comprise one or more additional
components that may enhance the stability of the device and/or
responsiveness of the device to ionizing radiation. In some cases,
the sensor material includes at least one additive that facilitates
interaction between the sensor material and ionizing radiation,
improves sensitivity for a particular type of ionizing radiation,
or otherwise enhances performance of the device. In some cases, the
additive may associate with the sensor material such that it
enhances an electrical, optical, or other property of the sensor
material. The additive may be positioned within the sensor material
such that interaction of the ionizing radiation with the additive
causes, enhances, or otherwise facilitates a determinable change in
signal upon exposure to an ionizing radiation. For example, a
sensor material may comprise an additive positioned in sufficient
proximity physically, or within sufficient electronic or inductive
communication range, to one or more components of the device able
to generate a signal. In some embodiments, the additive may be
covalently attached to a component (e.g., polymer material) of the
device, or may be dispersed within a component (e.g., sensor
material) of the device. In some embodiments, the sensor material
may comprise a plurality of additives.
[0046] The additive may be selected to enhance the sensitivity of
the interaction between the ionizing radiation and the sensor
material. For example, incorporation of a plurality of additives
within the device may improve the interaction between the sensor
material and the ionizing radiation, producing a large change in
signal. In some cases, the additive (e.g., a metal-containing
additive) may have high opacity to radiation, and may increase the
cross-section value of the sensor material for interaction with
ionizing radiation, such that a determinable signal may be
observed. The additive may be also selected to enhance the
selectivity of the interaction between the ionizing radiation and
the sensor material. For example, additives may be selected such
that the sensor material interacts with a particular type of
ionizing radiation to a greater extent than others, or with more
than one type of ionizing radiation. That is, the sensor material
may comprise additives which distinguish between different forms of
radiation (e.g., gamma rays, neutrons) present within a sample.
[0047] In some embodiments, the sensor material may comprise a
metal-containing group, such as a metal complex or a metal
nanoparticle. The metal-containing group may be selected to have a
high opacity for one or more types of ionizing radiation. In some
cases, the metal-containing group may have a high opacity for gamma
rays. In some cases, the metal-containing group may have a high
opacity for neutrons. For example, the metal may be selected to
have a high atomic number, as the cross-section values for the
interaction of gamma-rays with different elements increases with
increasing atomic number. In some embodiments, the metal-containing
group comprises a heavy metal. Incorporation of such additives
within the sensor material may increase the capture cross-section
and sensitivity of the device for one or more types of ionizing
radiation. In some embodiments, incorporation of an additive within
the sensor material may increase the sensitivity of the device to
ionizing radiation, or a specific type of radiation, by at least
about 5%, at least about 10%, at least about 20%, at least about
40%, at least about 60%, at least about 80%, at least about 100%,
at least about 200%, or greater.
[0048] In one set of embodiments, the metal-containing group
comprises bismuth. Bismuth (Bi) is the element with the highest
atomic number element that does not have naturally abundant
radioactive isotopes with short half lives. In some cases,
incorporating bismuth-containing species within the sensor material
may increase the opacity (e.g., cross-section) of the sensor
material towards radiation such as gamma rays. Bismuth may form
stable compounds with direct bismuth-carbon bonds, and the metal
centers may have relatively low coordination numbers. Species
comprising triphenyl bismuth, Bi(Ph).sub.3, for example, can be
readily synthesized. In some embodiments, a bismuth-containing
species may be incorporated into polymer materials described herein
using click chemistry, as described more fully below.
[0049] In another set of embodiments, the metal-containing group
comprises gadolinium. Gadolinium (Gd) has the second highest
cross-section for interaction with neutrons after .sup.135Xe and
gadolinium-containing species have been utilized as a relaxation
agent for creating contrast in MRI imaging. In some cases,
incorporation of gadolinium-containing species within the polymer
material may increase the opacity of the sensor material towards
neutrons. Various gadolinium-containing species may be designed and
synthesized using methods known in the art, including click
chemistry. As an illustrative embodiment, FIG. 5 shows a
gadolinium-containing compound that may be appended to an
azide-containing polymer via "click" chemistry.
[0050] Some embodiments may involve incorporation of metal
nanoparticles within the sensor material. In some cases,
nanoparticles of varying sizes may be incorporated into the device
to create differential responses to different energy radiation. As
used herein, the term "nanoparticle" generally refers to a particle
having a maximum cross-sectional dimension of less than about 10
.mu.m, less than about 5 .mu.m, or, in some cases, about 1 .mu.m or
less. In some embodiments, the nanoparticle may have a maximum
cross-sectional dimension of about 1 .mu.m (e.g., slightly more
than 1 .mu.m). Nanoparticles may comprise inorganic or organic,
polymeric, ceramic, semiconductor, metallic, non-metallic,
magnetic, crystalline (e.g., "nanocrystals"), or amorphous
material, or a combination of two or more of these. The
nanoparticles may be also selected to be positively or negatively
charged. Typically, nanoparticles may have a particle size less
than 250 nm in any dimension, less than 100 nm in any dimension, or
less than 50 nm in any dimension. In some embodiments, the
nanoparticles may have a diameter of about 2 to about 50 nm. In
some embodiments, the nanoparticles may have a diameter of about 2
to about 20 nm. The particle size may be measure by methods known
in the art, such as electron microscopy.
[0051] FIG. 11A shows a method for incorporating such nanoparticles
into the device, where a dispersion of polymer-coated bismuth
nanoparticle is formed. The polymer coating can be washed away and
the materials can be redispersed with other polymer coatings (e.g.,
POS coatings). Those of ordinary skill in the art would be able to
select other methods for incorporating nanoparticles into the
devices described herein. For example, as shown in FIG. 11B, the
affinity of Bi nanoparticle to thiols can be used to attach alkynes
to the surface of the nanoparticles. The alkyne-substituted
nanoparticles may then be reacted with azide-containing polymers
via click chemistry. Alternatively, nanoparticles may be
synthesized with an alternative polyamide containing an acetylene
endgroup, as shown in FIG. 11C.
[0052] Additives for facilitating processing and/or improving
stability of the device may also be incorporated into the sensor
material. In some embodiments, the sensor material may include a
species that can improve or enhance the compatibility (e.g.,
miscibility, solubility) of the various components of the sensor
material. Such additives may be useful in the formation of stable
nanostructure dispersions and/or films. For example, the sensor
material may comprise a plurality of nanostructures, a polymer
material in which the nanostructures are dispersed, and a species
capable of associating with nanostructures (e.g., carbon nanotubes)
to enhance the compatibility of the nanostructures with the polymer
material. In some cases, the species may interact with the
nanostructures via a bond, such as a covalent bond, an ionic bond,
a hydrogen bond (e.g., between hydroxyl, amine, carboxyl, thiol
and/or similar functional groups, for example), a dative bond (e.g.
complexation or chelation between metal ions and onodentate or
multidentate ligands), or the like. The interaction may also
comprise Van der Waals interactions. In some cases, the interaction
between the species and the nanostructure may comprise a
non-covalent bond. In some embodiments, non-covalent interactions
between the species and the nanostructures may be advantageous in
that the electronic structure of the nanostructures may not be
substantially affected (e.g., perturbed), and the high carrier
mobility of the nanostructures may be maintained.
[0053] In some embodiments, the species may interact with the
nanostructures via pi-pi-stacking interactions. Examples of such
species include aromatic moieties, such as polycyclic aromatic
hydrocarbons. In some embodiments, the sensor material comprises
pyrene groups, which are known to bind to the surface of a carbon
nanotube pi-pi stacking. The aromatic moieties may be covalently
bound to the polymer material, or may otherwise be associated with
the polymer material.
[0054] The polymer material may comprise any polymer having
sensitivity to ionizing radiation, i.e., any polymer that undergoes
a change in polymerization characteristic upon exposure to ionizing
radiation. For example, the polymer species may be depolymerized to
produce one or more volatile species that may be removed from the
device (e.g., via evaporation). In one set of embodiments, the
polymer material may comprise an optionally substituted poly(olefin
sulfone) (POS), which may undergo chain-scission and
depolymerization in the presence of ionizing radiation to produce
sulfur dioxide and an olefin species. POSs have been used as
electron beam resists and may degrade in the presence of ionizing
radiation (e.g., high energy electrons, gamma rays). Such polymers
may be synthesized via radical chain growth polymerization of
sulfur dioxide (SO.sub.2) and an olefin, as shown in FIG. 2. In
some cases, conditions for the synthesis of POSs involves bulk
polymerization at low temperatures with condensed liquid SO.sub.2
as the solvent and t-butyl hydroperoxide as the initiator. Polymers
obtained in this manner typically show a 1:1 ratio of perfectly
alternating sulfone and olefin units when there is an alkyl moiety
directly linked to the olefinic residue. Those of ordinary skill in
the art would be able to select the appropriate monomer species and
polymerization conditions suitable for use in a particular
application. In some cases, olefins used for polymerization is
electron-rich, sterically unhindered, non-basic, and/or is at least
partially solubility in SO.sub.2.
.DELTA.G=.DELTA.H-T.DELTA.S (Equation 1)
[0055] Thermodynamically, the polymerization to form POSs typically
proceeds (negative .DELTA.G in Eq. 1) at low temperature (T) due to
the decrease in entropy, a negative .DELTA.S term, in the
polymerization process. At higher temperature, the polymerization
may occur to a lesser degree, or not at all, since the -T.DELTA.S
term in Eq. 1 causes the polymerization to be endothermic (positive
.DELTA.G). The POS structures are kinetically stable at ambient and
even elevated temperatures because they are kinetically trapped by
strong bonds at the terminus of the polymer chains. Since these
bonds are not readily thermalized at temperatures of interest, the
materials can have good shelf life and can be used over a range of
conditions. However, once a chain is broken by a radiation induced
event the polymer rapidly depolymerizes into its monomeric
components. That is, the diffusion of monomer may advantageously
drive the depolymerization.
[0056] In some embodiments, the sensor material comprises a polymer
having the structure,
##STR00001##
wherein R is alkyl, heteroalkyl, alkenyl, heteroalkenyl, alkynyl,
heteroalkynyl, aryl, heteroaryl, any of which may be substituted;
and n is 1 or greater. In some embodiments, R is alkyl, optionally
substituted with an azide group or a polycyclic aromatic
hydrocarbon. In another embodiment, R is alkyl, optionally
substituted with COOR', wherein R' is H, alkyl, aryl, heteroalkyl,
heteroaryl, or a metal-containing species. In a particular
embodiment R' is a metal-containing complex or species (e.g.,
gadolinium).
[0057] In some cases, the sensor material comprises a polymer
having the structure,
##STR00002##
wherein R.sup.1 and R.sup.2 can be the same or different and are
alkyl, heteroalkyl, alkenyl, heteroalkenyl, alkynyl, heteroalkynyl,
aryl, heteroaryl, any of which may be substituted; m, n, and o can
be 0 or greater, provided that at least one of m, n, and o is 1 or
greater; and x is 1 or greater.
[0058] In some cases, the sensor material comprises one or more of
the following polymers,
##STR00003##
wherein R, R', and R'' may be the same or different and may be
alkyl, heteroalkyl, alkenyl, heteroalkenyl, alkynyl, heteroalkynyl,
aryl, heteroaryl, any of which may be substituted; a, b, c, d, and
e are 0 or greater; and m, n, and o can be 0 or greater, provided
that at least one of m, n, and o is 1 or greater; and x is 1 or
greater. In some embodiments, the sensor material comprises one or
more of the following polymers,
##STR00004##
The sensor material may also comprise a mixture of polymers, as
described more fully below.
[0059] In some embodiments, sensor material comprises the
polymer:
##STR00005##
wherein a, b, w, and n are each individually 0 or greater, R is
alkyl, aryl, heteroalkyl, heteroaryl, each optionally substituted.
In some cases, a, b, w, and n are each individually 1, or 2, or
greater. In some cases, a and b are 1, 2, 3, 4, or 5. In some
cases, a is 1 and b is 1, 2, 3, 4, 5. In some cases, R is alkyl,
for example, butyl. In some cases, w is 1, 2, 3, 4, 5, or in a
particular embodiment 1. A specific example of a polymer is:
##STR00006##
wherein a is 1, b is 3, and n is 40. The COOH group (or COO--
group) may be used to associate with a metal-containing complex or
species (e.g., gadolinium). For example, see Example 15.
[0060] In another example, the polymer material may comprise
optionally substituted polyaldehydes (PALs), which may depolymerize
in the presence of ionizing radiation to produce aldehyde species.
PALs, as shown in FIG. 8, are a class of thermodynamically
unstable, but kinetically stable, polymers, which can be
synthesized by anionic polymerization. Typically, PALs are
stabilized when the oxygen termini of the polymers are prevented
from depolymerization by endcapping reactions. As shown in FIG. 8,
polyaldehydes can be synthesized and then capped to create stable
compositions. Chain scission and depolymerization can be
accomplished through a radiation-induced ionization event. For
example, PAL chains may be depolymerized with an acid species. In
some cases, the acid may be generated in situ, as described more
fully below. The choice of endgroup can affect the sensitivity of
the polymer to acid. In the polymer shown in FIG. 8, the carbonate
end group may be cleaved in the presence of acid. Alternatively,
different choices of pendant groups (e.g., R groups) on the polymer
can also be used to adjust the acid sensitivity for optimizing
device stability.
[0061] Those of ordinary skill in the art would be able to select
the appropriate polymers suitable for use in a particular
invention. A simple screening test for the selection of polymer
material may be to expose a polymer to ionizing radiation and to
monitor the change in polymerization characteristic, or lack
thereof, of the polymer. For example, a polymer may be exposed to
ionizing radiation and may be monitored by optical spectroscopy, or
simply by sight, to determine if depolymerization occurs, i.e., if
the polymer depolymerizes into volatile monomeric species, which
then evaporate.
[0062] In some embodiments, the polymer material may be tailored to
have enhanced sensitivity to ionizing radiation. For example,
polymer materials that readily depolymerize upon exposure to
ionizing radiation may be designed and synthesized. That is,
polymers having a relatively lower polymerization ceiling
temperature (T.sub.C) may be selected for use in the device. The
addition of substituents in the polymer backbone can be a highly
effective means to lower the ceiling temperature and, as shown in
Table 1, copolymers of 2-methyl-1-pentene exhibit a dramatically
lower T.sub.C as compared to other POS materials. FIG. 7 shows an
example of a poly(olefin sulfone) incorporating 2-methyl-1-pentene.
Without wishing to be bound by theory, this effect may be
attributed to the increased steric congestion about the polymer
backbone and the interactions between the sulfone groups and the
alkyl groups are illustrated in FIG. 7. In some cases,
polymerization of these materials are carried out at lower
temperatures, and, once synthesized, the materials are kinetically
stable to temperatures over 100.degree. C. Using such materials,
the rate of depolymerization upon radiation-induced chain scission
of such materials may be increased.
TABLE-US-00001 TABLE 1 Ceiling temperatures for POS materials
synthesized by copolymerization of the olefin shown with SO.sub.2.
Olefin Monomer Tc (.degree. C.) 1-butene 62 1-pentene 44.5 1-hexene
60 1-hexadecene 48.5 2-methyl-1-pentene -32.5 3-methyl-1-butene
36.5
[0063] In one set of embodiments, the sensor material may comprise
a mixture of polymers, each polymer capable of undergoing a change
in a polymerization characteristic upon exposure to ionizing
radiation. In some cases, a multistage, cascade event may occur,
where a change in a polymerization characteristic of a first
polymer may cause a change in a polymerization characteristic of a
second polymer. For example, the sensor material may comprise a
first polymer and a second polymer, and exposure to ionizing
radiation results in depolymerization of the first polymer to
produce an initiator species, which may then interact with the
second polymer to result in depolymerization of the second
polymer.
[0064] FIG. 9 shows an illustrative embodiment of a multistage
cascade event that may be utilized in the context of the invention.
In the case of POSs, a single chain scission event may generate
many equivalents of SO.sub.2, which may either escape from the
material as a gaseous material or may be oxidized (e.g., by metal
oxides like V.sub.2O.sub.5) to generate sulfuric acid
(H.sub.2SO.sub.4), which can catalyze the depolymerization of PAL
materials. Due to this catalytic activity, one equivalent of the
acid may depolymerize a number of PAL chains. Thus, a multistage
cascade event may occur, wherein a single ionization event creates
many (n) molecules of SO.sub.2, and each SO.sub.2 creates a
molecule of acid, which in turn catalyzed a multitude (y) of
depolymerized PALs with each polymer liberating n' equivalents of
aldehyde. In some cases, n.apprxeq.100, y.apprxeq.10,
n'.apprxeq.100, and 10.sup.5 equivalents of monomer may be released
from a single chain scission event. In this way, systems capable of
high sensitivity to ionization events may be realized.
[0065] Those of skill in the art would be able to identify other
materials having complementary reactivity to perform such a cascade
reaction. For example, the materials may be selected such that a
first polymer is capable of producing a species that may catalyze
depolymerization of a second polymer.
[0066] In another set of embodiments, the sensor material may
comprise an additive that may interact with ionizing radiation to
produce an initiator species. The initiator species may then
interact with a polymer material, or portion thereof, to cause a
change in a polymerization characteristic of the polymer material
(e.g., depolymerization). For example, one method for generating an
initiator species, such as an acid, either directly or indirectly
from a radiation event is to employ initiators used in chemically
amplified lithography. In this method, stable cationic complexes
may be placed into a polymer matrix, where exposure to light
creates a strong acid. FIG. 10 shows examples of various additives
that are capable of generating initiator species upon exposure to
radiation. Other photoacid generators or photoresist additives may
also be used in the context of this invention, where
photoexcitation of a cationic acid precursor results in their
reduction by electron transfer processes. In the case of the iodine
containing photoacid generators, the heavy atoms may help to
increase the reactive cross-section.
[0067] Some devices may be fabricated such that two or more
different types of ionizing radiations may be determined. In some
cases, the sensor material may include a gradient of materials
capable of determining a wide range of radiation. That is, the
device may comprise components that may specifically interact with
various types of ionizing radiations. For example, the sensor
material may include a plurality of metal-containing groups, each
group having a different cross-section value for interaction with
ionizing radiation. In some cases, the device may be fabricated
such that it includes at least two different types of species
(e.g., metal atoms or nanoparticles), each selected to interact
with a specific type of ionizing radiation, such that various
changes in the signal(s) produced by the device may be attributed
to a particular form of ionizing radiation. The species may differ
in chemical structure, size, or other properties. In an
illustrative embodiment, the sensor material may comprise both
bismuth atoms or nanoparticles, which may enhance the opacity of
the sensor material to gamma rays, and gadolinium atoms or
nanoparticles, which may enhance the opacity of the sensor material
to neutrons. It should be understood that the device may contain
any number of additives for determining ionizing radiation.
[0068] In another set of embodiments, a system may include an array
of individual devices having varying levels of sensitivity to
different types of radiation, creating a spectrometer that can
identify more than one type of radiation. Array devices can be
created, for example, for spectroscopic detection of gamma rays of
different energies, or for discrimination between thermal and fast
neutrons. In a particular embodiment, devices capable of detecting
radiation as part of distributed sensor arrays are provided.
Distributed arrays can be used to monitor transportation systems,
shipping containers, or distributed in other areas of interest. In
addition to non-proliferation applications, these devices can have
applications in occupational safety and will enable individuals to
know immediately if they are being exposed to radiation.
[0069] The devices described herein may comprise additional
components, such as a signal generator that generates a signal
responsive to a change in polymerization characteristic, and a
detector component positioned to detect the signal. In one set of
embodiments, the device may be a chemiresistor device, wherein the
device exhibits changes in electrical resistance upon exposure to
an ionizing radiation. Chemiresistors may be advantageous in that
the resistance changes can be read-out by a simple, low power and
low current circuit. In other embodiments, a device of the present
invention may exhibit signals, or changes in signals, that may be
determined using Raman spectroscopy, adsorption and/or emission
photophysics, ellipsometry, atomic force microscopy, scanning
electron microscopy, electrode passivation, and the like.
[0070] As described herein, the polymer material may be
functionalized with one or more species to improve performance of
the device. In some embodiments, a modular approach to the
functionalization of polymer materials is provided, allowing for
the integration of a wide range of functionality into the polymer
matrix. For example, the method may involve use of a polymer or
monomer species capable of reacting via a 1,3-dipolar cycloaddition
reaction, i.e., via "click chemistry." That is, a polymer or
monomer species may comprise a dipolarophile group (e.g., an
alkyne) that is reacted with a 1,3-dipolar compound. Alternatively,
a polymer or monomer species may comprise a 1,3-dipolar compound
(e.g., an azido group) that is reacted with a dipolarophile. In
some embodiments, functionalization may be performed prior to
formation of the polymer, i.e., functionalization of a monomer
species may be performed. In some embodiments, functionalization
may be performed after formation of the polymer, i.e.,
functionalization of a polymer species may be performed.
[0071] The 1,3-dipolar cycloaddition reaction may be performed
under conditions that may be unreactive to the remainder of the
species other than the dipolarophile or 1,3-dipolar compound. In an
illustrative embodiment, a polymer material may contain an azido
group, which may be further reacted with an alkyne species to form
a triazole group. Such a strategy may be useful, for example, for
incorporating various groups or additives described herein into a
polymer material. Those of ordinary skill in the art would be able
to select the appropriate reaction conditions and additives
suitable for a particular 1,3-dipolar cycloaddition reaction.
Methods for performing 1,3-dipolar cycloaddition reactions are also
described, for example, in Synthetic Applications of 1,3-Dipolar
Cycloaddition Chemistry Toward Heterocycles and Natural Products,
A. Padwa, W. H. Pearson, Wiley-Interscience, 2002, the contents of
which are incorporated herein by reference.
[0072] In one set of embodiments, a series of azide-containing
poly(olefin sulfone)s may be synthesized. (FIG. 3) In some
embodiments, the composition of the resulting polymers may be the
same as the feed ratio, indicating that quantity of azides in a
polymer can be perfectly controlled, as shown in the table in FIG.
3 and FIG. 18. In some cases, the polymerization may advantageously
have a random sequence of monomer units.
[0073] In some embodiments, the method involves synthesis of a
polymer comprising the structure,
##STR00007##
wherein n is 1 or greater, following by reaction of the polymer
with at least one type of alkyne-containing species. The
alkyne-containing species may comprise any of the additives
described herein, including metal-containing species, aromatic
groups, and the like. FIG. 4A illustrates examples of
alkyne-containing species that may be reacted with the polymer via
"click" chemistry. The degree of functionalization of the polymer
may be controlled, based on the quantity of azides in the polymer
starting material.
[0074] In some embodiments, the method involves synthesis of a
polymer comprising the structure,
##STR00008##
wherein p is 1 or greater (e.g., 1, 2, 3, 4, 5, etc.) and v is 0 or
greater (e.g., 0, 1, 2, 3, 4, 5, etc.). In some cases, v is 0 or 1.
Methods for synthesizing such polymers will be known to those of
ordinary skill in the art (e.g., see Example 15).
[0075] Methods for determining ionizing radiation are also
provided. As used herein, the term "determining" generally refers
to the analysis of a species or signal, for example, quantitatively
or qualitatively (whether an analyte is present and/or in what
amount or concentration), and/or the detection of the presence or
absence of the species or signals. "Determining" may also refer to
the analysis of an interaction between two or more species or
signals, for example, quantitatively or qualitatively, and/or by
detecting the presence or absence of the interaction. For example,
the method may include the use of a device capable of producing a
first, determinable signal (e.g., a reference signal), such as an
electrical signal, an optical signal, or the like, in the absence
of ionizing radiation. The device may then be exposed to ionizing
radiation, wherein the ionizing radiation may interact with one or
more components of the device to cause a change in the signal
produced by the device. Determination of the change in the signal
may then determine the analyte. The signal may, in some cases,
provide information relating to the presence, identity, amount,
and/or other characteristic of the ionizing radiation.
[0076] In some embodiments, the change in signal may occur upon
interaction between ionizing radiation and at least a portion or
component of the device. For example, the ionizing radiation may
contact or may permeate an interior portion of the sensor material.
In some embodiments, a volumetric or dimensional change (e.g.,
increase, decrease) of the sensor material may occur upon
interaction with an analyte. In some cases, the interaction between
the sensor material and the ionizing radiation may comprise a
reaction, such as a depolymerization reaction. For example, the
method may involve exposure of the device to an environment
suspected of containing ionizing radiation, wherein the ionizing
radiation, if present, interacts with the polymer material such
that at least a portion of the polymer material undergoes a change
in a polymerization characteristic, which generates a determinable
signal. In some cases, exposure of the device to an environment
suspected of containing ionizing radiation, results in a change in
the average distance between adjacent nanostructures, which
generates a determinable signal. Determination of the signal may
then determine the ionizing radiation.
[0077] In some embodiments, the device comprises a first electrode
and a second electrode in electrochemical communication with the
sensor material, such that the determinable signal comprises a
change in resistance to current flow between the first and second
electrodes. For example, the resistance may decrease upon exposure
to ionizing radiation. In some cases, methods described herein may
determine an ionizing radiation with relatively high selectivity
and/or specificity. For example, the device may comprise a sensor
material that is responsive to a particular type of ionizing
radiation and is substantially unresponsive to other types of
ionizing radiation or is responsive to a lesser degree, such that
the change in signal may be attributed to an interaction between
the sensor material and the particular type of ionizing radiation.
In some cases, the method may involve determination of more than
one type of ionizing radiation present within a sample. For
example, the interaction between a first type of ionizing radiation
and the sensor material may give a first change in the properties
(e.g., electrical properties) of the sensor material, while the
interaction between a second type of ionizing radiation and the
sensor material may give a second, different change in the
properties of the sensor material, such that distinguishable
changes in signal may be determined for both the first and second
types of ionizing radiation.
[0078] In some cases, the ionizing radiation may produce a
colorimetric change within the device, wherein observation of a
visible change in color may determine the analyte. In some
embodiments, the ionizing radiation may produce a change in an
absorption or luminescence spectrum of the device. For example,
metal nanoparticles (e.g., silver and/or gold nanoparticles) may be
incorporated within the sensor material to create sensors that
provide a visual signal to radiation. In these schemes the small
particle sizes may give rise to plasmon absorptions that can give
rise to strong colors. For example, for small gold nanoparticles
with diameters around 13 nm, these absorptions give rise to
materials that have a red appearance when the particles are
isolated that shifts to blue when the particles are aggregated.
[0079] Quantification of the sensitivity in these devices may be
performed by absorbance spectroscopy. The change in a peak and/or
trough of the spectrum may be measured, for example, by addition,
subtraction, multiplication, or division of the spectra, or by
observation of a change in the distance between peaks and/or
troughs of the spectra, a change in the shape of the spectra,
and/or the like. In some cases, the change in signal may be
determined using an analyzer that may compare the signals produced
by the device before and after exposure to an analyte. In some
cases, the signals may be further processed to determine the
analyte. For example, the signal may be filtered, amplified,
subject to Fourier transforms, decomposed using wavelet
decomposition, and/or the like.
[0080] Devices of the invention may be fabricated using methods
described herein, and/or in combination with other methods known to
those of ordinary skill in the art. In some embodiments, methods of
the invention may advantageously provide the ability to process
materials which may otherwise be insoluble and/or difficult to
process. For example, the method may allow for the formation of
stable dispersions of nanostructures, such that the nanostructures
are readily processible in solution. In some cases, the method may
involve processing a mixture comprising a plurality of
nanostructures (e.g., carbon nanotubes) and a polymer material, or
precursor thereof, to form a sensor material as described herein.
The mixture may be a solution, a suspension, a dispersion, or the
like. In some cases, the polymer material may have a relatively
high molecular weight. In some cases, a dispersion of
nanostructures may be stable under ambient atmosphere, at room
temperature, and/or for long periods of time (e.g., several weeks,
months, or years).
[0081] In certain embodiments, the polymer material and carbon
nanotubes are mixed with a fluid carrier to form a solution,
suspension, dispersion, etc. That is, the polymer material and/or
carbon nanotubes may, in some cases, are soluble in a fluid
carrier. In some cases, the polymer material and/or carbon
nanotubes are not soluble in the fluid carrier. The mixture may
comprise any common fluid carrier (e.g., solvent) known to those of
common skill in the art such as tetrahydrofuran, chloroform, and
the like. In some cases, the solution may comprise more than one
fluid carrier. In some cases, the mixture of the polymer material
and the carbon nanotubes may be sonicated to facilitate formation
of a dispersion. Other methods for the formation of nanostructure
dispersions are described in International Pat. Apl. Serial No.:
PCT/US2009/001396, filed Mar. 4, 2009, entitled, "Devices and
Methods for Determination of Species Including Chemical Warfare
Agents" and U.S. application Ser. No. 12/474,415, filed May 29,
2009, entitled, "Field Emission Devices Including Nanotubes or
Other Nanoscale Articles," which are incorporated herein by
reference in their entirety for all purposes.
[0082] The mixture may be processed by various methods, including
spin-coating, drop-casting, spray-coating, ink jet printing,
electrophoretic deposition, medium scale deposition using a doctor
knife, continuous processes and the like. In some cases, the sensor
material may be formed (e.g., deposited) on a substrate, including
an electrode (e.g., interdigitated electrodes), an integrated
device, an integrated circuit, or the like. In some embodiments,
the sensor material may be formed on patterned electrode
assemblies. The deposition of metal electrodes may also be
performed using known methods, such as evaporation and sputter
coating. Array devices for the discrimination of different types of
radiation can be created by, for example, ink jet printing of
suspensions comprising the nanostructures, polymer material, and/or
any additives (e.g., nanoparticles) on circuitry. For distributed
sensory arrays the low power requirements of the devices may be
compatible with RFID methods. This versatility may allow for the
economical manufacture of devices at any size and in various
configurations.
[0083] In some embodiments, at least a portion of the sensor
material (e.g., polymer material) may be used as an electron beam
resist, allowing for the use of electron-beam lithography to create
nano-circuits in the device. Using this approach, gaps between
conductive regions that need to be activated to create increased or
decreased conductance may be reduced. Interdigitated devices, as
shown in FIG. 12, may include many small gaps, including submicron
gaps, and may generate large signals. In cases where submicron gaps
are utilized, the nanostructures may be selected to have dimensions
compatible with the submicron gaps. For example, shortened carbon
nanotubes may be employed. In addition, any shape for the
conductive network may be utilized to allow different regions of a
device to be addressed.
[0084] In some embodiments, the sensor material may have high
mechanical integrity and can be processed as free-standing films.
For example, the sensor material may be removed from a surface by
immersion in water, as shown in FIG. 6. The atomic force microscopy
(AFM) images of FIG. 6 show a single-walled carbon nanotube
(SWCNT)/polymer thin film, (a) as cast and (b) after extraction of
the polymer more clearly showing the SWCNT network; (c) an optical
image of SWCNT/polymer film deposited on glass slides; (d) a
free-standing SWCNT/polymer film floating on water surface; and (e)
a SWCNT/polymer film transferred on silicon substrate. An advantage
of this method is that the materials can be placed on a diverse
array of substrates, including plastics that may not be compatible
with the solvents used in the initial fabrication.
[0085] In some cases, the mixture may be processed to form a thin
film comprising the carbon nanotubes and the polymer material. A
thin film may have a thickness between about 0.1 nm and about 100
um. For example, the thickness of the film may be less than about
100 um, less than about 50 um, less than about 25 um, less than
about 10 um, less than about 5 um, less than about 1 um, less than
about 500 nm, less than about 250 nm, less than about 100 nm, less
than about 50 nm, less than about 25 nm, less than about 10 nm,
less than about 5 nm, less than about 2 nm, less than about 1 nm,
or in some cases, less than about 0.5 nm. The thickness of the film
may or may not be uniform throughout the device. A thin film may be
formed using processes such as spin-on methods, chemical vapor
deposition, pulsed laser deposition, vacuum plasma spray, wet
spray, sputtering, evaporation, or molecular beam epitaxy.
[0086] In some cases, device sensitivity may be increased by
application of strain to the sensor material (e.g., in film form).
For example, chemical crosslinks may be introduced into sensor
materials with low glass transition temperatures post-casting to
create an elastomeric film that undergo minimal or substantially no
plastic flow over time. Application of mechanical stress to the
films may result in the alignment of nanostructures and decrease
the electrical resistance in the stretch direction. In some cases,
a percolated SWCNT network may form in the stretching direction.
Cleavage of the polymer matrix may allow for relaxation of the
network and the SWCNTs orientation may commensurately relax and
effectively break the circuit. In this scheme, a fuse that breaks
in response to radiation is essentially formed.
[0087] Another method for creating strained systems, which can be
applied to freestanding or surface confined films, may be to swell
the crosslinked materials with another liquid. Both methods (e.g.,
swelling and mechanical stretching) may stress the polymer matrix,
placing the polymer in a high-energy conformational state. However,
mechanical stretching may result in a densification of the material
and swelling fundamentally expands the matrix. In the swelling
schemes, materials in which the unstressed compositions are
conductive and have a percolative network of SWCNTs may be used.
Swelling of the films may then disrupt the percolative network of
SWCNTs and lower the conductance. Cleavage of the polymer chains
may allow for relaxation of the network and re-establishment of
connections between nanostructures (e.g. carbon nanotubes). A
variety of fluids can be utilized, including materials with heavy
atoms. In some embodiments, ionic liquids are used, as they
typically do not evaporate over extended periods and allow for a
diversity of counterions.
[0088] The application of strain may give additional intrinsic
sensitivity to the devices as a result of the strain applied to the
polymer chains. For example, with any radiation-induced chain
cleavage there may be some unproductive events wherein the two
reactive units generated by scission of a polymer chain can
recombine. When the polymers are placed under stress, rapid
relaxation to a lower energy conformation may prevent the
recombination process. In some cases, cleavage of a few polymer
chains can place strains on adjacent polymers. These strains can be
so large that the adjacent polymers may fragment and cause further
depolymerization (e.g., a cascade process).
[0089] The method may further comprise forming at least one
electrode material, for example, on the surface of a substrate or
in contact with the sensor material. In some cases, at least two
electrode materials, or more, are formed on the surface of a
substrate or in contact with the sensor material. The electrode
materials, and other components of the device, may be formed at any
time during the fabrication process to produce devices as described
herein, or devices having an alternative arrangement. For example,
the sensor material, electrode materials(s) (e.g., source
electrode, drain electrode, gate electrode, etc.), and/or an
insulating material may be fabricated in any order to produce a
device as described herein. In some embodiments, the electrode
material may be formed on a substrate prior to formation of the
sensor material. In some embodiments, the electrode may be formed
on the sensor material. The electrode material(s) may be deposited
onto any component of the device using methods known in the art,
such as electroplating.
[0090] In some embodiments, simple screening tests may be conducted
to select appropriate sensor materials (e.g., carbon nanotubes,
polymer material, etc.), additives, device configuration, set of
conditions, etc., to suit a particular application. In some cases,
a material or device may be screened to determine the sensitivity
and/or stability of the material or device. In some cases, a
material (and/or device) may be selected based on an ability to
detect one or more types of radiation. For example, the ability of
a device to detect ionizing radiation may be determined by
comparing the signal (e.g., conductance) of the device prior to and
following exposure to ionizing radiation. In another example, a
device may be exposed to varying concentrations of ionizing
radiation to determine the sensitivity of the device. As another
example, a first device and a second device may be provided,
wherein the second device comprises a different material (e.g.,
nanostructure, polymer material, additive, electrode material,
etc.) and/or configuration (e.g., relative position of components,
or additional component such as a gate electrode or insulating
material, etc.) as compared to the first device. Signals produced
by the first and second devices prior to and following exposure to
ionizing radiation (e.g., percent change in signal upon exposure to
ionizing radiation, baseline signal, time required for following
exposure to the analyte for the signal to return to baseline, etc.)
may then be compared to determine differences between the
performance of first and second devices.
[0091] As described herein, a system comprising two or more devices
may be fabricated, wherein each device comprises a first electrode,
a second electrode and a sensor material comprising carbon
nanotubes dispersed in a polymer material. In some cases, the
individual devices of the system may be substantially identical.
For example, the individual devices may be constructed to interact
with the same form of ionizing radiation. In some cases, the
individual devices of the system may be different, such that each
individual device may selectively interact with a particular type
of ionizing radiation. This may be accomplished, for example, by
fabricating a plurality of devices, each comprising a sensor
material and/or binding site responsive to a different type of
ionizing radiation. For example, each individual device may be
capable of interacting with a particular type of ionizing
radiation, and may interact with other types of ionizing radiation
to a different (e.g., lesser) extent. This may be useful in
determining two or more different types of ionizing radiation
present in a single sample.
[0092] Devices as described herein may have various device
configurations, and may be selected to suit a particular
application. For example, the sensor material may be fabricated
such that a first and the second electrode are in electrochemical
communication with the sensor material. "Electrochemical
communication," as used herein, refers to materials that are in
sufficient communication with each other, such that the transfer of
electrons and/or protons and/or other charged moieties can occur
between the two materials. For example, the first and second
electrodes may not contact one another but may be in
electrochemical communication with one another via the sensor
material, such that upon application of a voltage between the first
and second electrode, a current flows from the one electrode
through the sensor material to the other electrode. In some
instances, the first electrode may be a source electrode and the
second electrode may be a drain electrode. In some instances, the
sensor material is placed on a substrate. Non-limiting embodiments
of devices are described more fully below.
[0093] As used herein, the term "nanostructure" refers to any
chemical structure having at least one dimension on the order of
nanometers. In some cases, the nanostructure has an elongated
chemical structure having a diameter on the order of nanometers and
a length on the order of microns to millimeters, resulting in an
aspect ratio greater than 10, 100, 1000, 10,000, or greater. In
some cases, the nanostructure may have a diameter less than 1
.mu.m, less than 100 nm, 50 nm, less than 25 nm, less than 10 nm,
or, in some cases, less than 1 nm. The nanostructure may have a
cylindrical or pseudo-cylindrical shape. In some cases, the
nanostructure may be a nanotube, such as a carbon nanotube. In some
cases, the nanostructure is a nanorod, nanowire, or nanoribbon. In
some cases, the nanostructure is a nanoparticle.
[0094] As used herein, the term "carbon nanotube" is given its
ordinary meaning in the art and refers to a substantially
cylindrical molecule, in some cases, comprising a fused network of
six-membered aromatic rings. In some cases, carbon nanotubes may
resemble a sheet of graphite rolled up into a seamless cylindrical
structure. It should be understood that the carbon nanotube may
also comprise rings other than six-membered rings. Typically, at
least one end of the carbon nanotube may be capped, i.e., with a
curved or nonplanar aromatic group. Carbon nanotubes may have a
diameter of the order of nanometers and a length on the order of
millimeters, resulting in an aspect ratio greater than about 100,
greater than about 1000, greater than about 10,000, or greater. The
term "carbon nanotube" includes single-walled nanotubes (SWCNTs),
multi-walled nanotubes (MWCNTs) (e.g., concentric carbon
nanotubes), inorganic derivatives thereof, and the like. In some
embodiments, the carbon nanotube is a single-walled carbon
nanotube. In some cases, the carbon nanotube is a multi-walled
carbon nanotube (e.g., a double-walled carbon nanotube).
[0095] The carbon nanotubes may be functionalized or substituted
with a wide range of functional groups. Examples of functional
groups that carbon nanotubes may be substituted with include
peptides, proteins, DNA, RNA, peptide nucleic acids (PNA), metal
complexes, ligands for metals, ligands for proteins, antibodies,
polarizable aromatics, crown ethers, hydroxylamines, polymers,
initiators for polymerizations, liquid crystals, fluorocarbons,
synthetic receptors, and the like. The properties of the nanotubes
may also be tailored based on the substitution of the fused,
aromatic network. Those skilled in the art would recognize what
types of functional groups would afford a particular, desired
property, such as increased solubility, or the ability to determine
an analyte. In some embodiments, the substituted carbon nanotube
comprises a binding site. In some embodiments, substituted carbon
nanotubes may be readily processed in a fluid carrier. That is,
dispersions of substituted carbon nanotubes may be formed.
[0096] Substituted carbon nanotubes may be synthesized using
various methods, including those described in Zhang et al., J. Am.
Chem. Soc. 2007, 129(25), 7714; International Publication No.
WO2008/1337791, which are incorporated herein by reference in their
entirety for all purposes.
[0097] Polymers or polymer materials, as used herein, refer to
extended molecular structures comprising a backbone (e.g.,
non-conjugated backbone, conjugated backbone) which optionally
contain pendant side groups, where "backbone" refers to the longest
continuous bond pathway of the polymer. In some embodiments, the
polymer is substantially non-conjugated or has a non-conjugated
backbone. In some embodiments, at least a portion of the polymer is
conjugated, i.e. the polymer has at least one portion along which
electron density or electronic charge can be conducted, where the
electronic charge is referred to as being "delocalized." A polymer
may be "pi-conjugated," where atoms of the backbone include
p-orbitals participating in conjugation and have sufficient overlap
with adjacent conjugated p-orbitals. It should be understood that
other types of conjugated polymers may be used, such as
sigma-conjugated polymers.
[0098] In one embodiment, the polymer is selected from the group
consisting of poly(olefin sulfone)s or polyaldehydes.
[0099] The polymer can be a homo-polymer or a co-polymer such as a
random co-polymer or a block co-polymer. In one embodiment, the
polymer is a block co-polymer. An advantageous feature of block
co-polymers is that they may mimic a multi-layer structure, wherein
each block may be designed to have different band gap components
and, by nature of the chemical structure of a block co-polymer,
each band gap component is segregated. As described herein, the
band gap and/or selectivity for particular analytes can be achieved
by modification or incorporation of different polymer types. The
polymer compositions can vary continuously to give a tapered block
structure and the polymers can be synthesized by either step growth
or chain growth methods.
[0100] The number average molecular weight of the polymer may be
selected to suit a particular application. As used herein, the term
"number average molecular weight (M.sub.n)" is given its ordinary
meaning in the art and refers to the total weight of the polymer
molecules in a sample, divided by the total number of polymer
molecules in a sample. Those of ordinary skill in the art will be
able to select methods for determining the number average molecular
weight of a polymer, for example, gel permeation chromatography
(GPC). In some cases, the GPC may be calibrated vs. polystyrene
standards. In some cases, the number average molecular weight of
the polymer is at least about 10,000, at least about 20,000, at
least about 25,000, at least about 35,000, at least about 50,000,
at least about 70,000, at least about 75,000, at least about
100,000, at least about 110,000, at least about 125,000, or
greater.
[0101] In some embodiments, various components of the device are
formed on a substrate. The substrate can comprise a wide variety of
materials, as will be appreciated by those in the art, including
printed circuit board (PCB) materials. Suitable substrates include,
but are not limited to, fiberglass, Teflon, ceramics, glass,
silicon, mica, plastic (including acrylics, polystyrene and
copolymers of styrene and other materials, polypropylene,
polyethylene, polybutylene, polycarbonate, polyurethanes, and
derivatives thereof, etc.), GETEK (a blend of polypropylene oxide
and fiberglass), and the like. The device may also comprise an
insulating material. The insulating material may be arranged
between the sensor material and one or more electrodes (e.g., gate
electrode) and/or the substrate. In some cases, the insulating
material may reduce the mobile ion damage and minimize drift in gas
sensor devices and/or may improve physical adhesion of the sensor
material to the underlying material or substrate. Examples of
suitable insulating materials include, but are not limited to,
polysilicate glass, silicon dioxide, silicon nitride, and the
like.
[0102] As used herein, the term "electrode" or "electrode material"
refers to a composition, which, when connected to an electronic
device, is able to sense a current or charge and convert it to a
signal. An electrode may be comprised of a conductive material or
combination of materials such as, for example, metals. Non-limiting
examples of suitable metals include gold, copper, silver, platinum,
nickel, cadmium, tin, and the like. The electrodes may also be any
other metals and/or non-metals known to those of ordinary skill in
the art as conductive (e.g. ceramics). The electrodes may be
deposited on a surface via vacuum deposition processes (e.g.,
sputtering and evaporation) or solution deposition (e.g.,
electroplating or electroless processes). In a specific example,
gold electrodes are deposited by sputter-coating.
[0103] As used herein, the term "environment" refers to any medium
(e.g., solid, liquid, gas) that can be evaluated in accordance with
the invention including, such as air or other vapor samples, soil,
water, a biological sample, etc. An "environment suspected of
containing" a particular component means a sample with respect to
which the content of the component is unknown. For example, a gas
environment where one or more forms of ionizing radiation may be
present, but not known to have the ionizing radiation, defines a
sample suspected of containing ionizing radiation.
[0104] As used herein, the term "alkyl" is given its ordinary
meaning in the art and may include saturated aliphatic groups,
including straight-chain alkyl groups, branched-chain alkyl groups,
cycloalkyl (alicyclic) groups, alkyl substituted cycloalkyl groups,
and cycloalkyl substituted alkyl groups. In certain embodiments, a
straight chain or branched chain alkyl has about 30 or fewer carbon
atoms in its backbone (e.g., C.sub.1-C.sub.30 for straight chain,
C.sub.3-C.sub.30 for branched chain), and alternatively, about 20
or fewer. Likewise, cycloalkyls have from about 3 to about 10
carbon atoms in their ring structure, and alternatively about 5, 6
or 7 carbons in the ring structure. In some embodiments, an alkyl
group may be a lower alkyl group, wherein a lower alkyl group
comprises 10 or fewer carbon atoms in its backbone (e.g.,
C.sub.1-C.sub.10 for straight chain lower alkyls).
[0105] The term "heteroalkyl" is given its ordinary meaning in the
art and refers to alkyl groups as described herein in which one or
more atoms is a heteroatom (e.g., oxygen, nitrogen, sulfur, and the
like). Examples of heteroalkyl groups include, but are not limited
to, alkoxy, poly(ethylene glycol)-, alkyl-substituted amino,
tetrahydrofuranyl, piperidinyl, morpholinyl, etc.
[0106] The term "aryl" is given its ordinary meaning in the art and
refers to single-ring, multiple-ring, or multiple-fused-ring
aromatic groups comprising, for example, 5-, 6- and 7-membered ring
aromatic groups, all optionally substituted. In some cases, the at
least one ring in the aryl group is aromatic. The term "heteroaryl"
is given its ordinary meaning in the art and refers to aryl groups
as described herein in which one or more atoms is a heteroatom
(e.g., oxygen, nitrogen, sulfur, and the like). Examples of aryl
and heteroaryl groups include, but are not limited to, phenyl,
pyrrolyl, furanyl, thiophenyl, imidazolyl, oxazolyl, thiazolyl,
triazolyl, pyrazolyl, pyridinyl, pyrazinyl, pyridazinyl and
pyrimidinyl, and the like. It should be understood that, when aryl
and heteroaryl groups are used as ligands coordinating a metal
center, the aryl and heteroaryl groups may have sufficient ionic
character to coordinate the metal center.
[0107] The terms "carboxyl group," "carbonyl group," and "acyl
group" are recognized in the art and can include such moieties as
can be represented by the general formula:
##STR00009##
wherein W is H, OH, O-alkyl, O-alkenyl, or a salt thereof. Where W
is O-alkyl, the formula represents an "ester." Where W is OH, the
formula represents a "carboxylic acid." The term "carboxylate"
refers to an anionic carboxyl group. In general, where the oxygen
atom of the above formula is replaced by sulfur, the formula
represents a "thiolcarbonyl" group. Where W is a S-alkyl, the
formula represents a "thiolester." Where W is SH, the formula
represents a "thiolcarboxylic acid." On the other hand, where W is
alkyl, the above formula represents a "ketone" group. Where W is
hydrogen, the above formula represents an "aldehyde" group.
[0108] As used herein, the term "halogen" or "halide" designates
--F, --Cl, --Br, or --I.
[0109] The term "alkoxy" refers to the group, --O-alkyl.
[0110] The term "aryloxy" refers to the group, --O-aryl.
[0111] The term "acyloxy" refers to the group, --O-acyl.
[0112] The term "arylalkyl", as used herein, refers to an alkyl
group substituted with an aryl group.
[0113] The terms "amine" and "amino" are art-recognized and refer
to both unsubstituted and substituted amines, e.g., a moiety that
can be represented by the general formula: N(R')(R'')(R''') wherein
R', R'', and R''' each independently represent a group permitted by
the rules of valence.
[0114] As used herein, the term "substituted" is contemplated to
include all permissible substituents of organic compounds,
"permissible" being in the context of the chemical rules of valence
known to those of ordinary skill in the art. In some cases,
"substituted" may generally refer to replacement of a hydrogen atom
with a substituent as described herein. However, "substituted," as
used herein, does not encompass replacement and/or alteration of a
key functional group by which a molecule is identified, e.g., such
that the "substituted" functional group becomes, through
substitution, a different functional group. For example, a
"substituted phenyl" group must still comprise the phenyl moiety
and cannot be modified by substitution, in this definition, to
become, e.g., a cyclohexyl group. In a broad aspect, the
permissible substituents include acyclic and cyclic, branched and
unbranched, carbocyclic and heterocyclic, aromatic and nonaromatic
substituents of organic compounds. Illustrative substituents
include, for example, those described herein. The permissible
substituents can be one or more and the same or different for
appropriate organic compounds. For example, a substituted alkyl
group may be CF.sub.3. For purposes of this invention, the
heteroatoms such as nitrogen may have hydrogen substituents and/or
any permissible substituents of organic compounds described herein
which satisfy the valencies of the heteroatoms. This invention is
not intended to be limited in any manner by the permissible
substituents of organic compounds.
[0115] Examples of substituents include, but are not limited to,
alkyl, aryl, arylalkyl, cyclic alkyl, heterocycloalkyl, hydroxy,
alkoxy, aryloxy, perhaloalkoxy, arylalkoxy, heteroaryl,
heteroaryloxy, heteroarylalkyl, heteroarylalkoxy, azido, amino,
halogen, alkylthio, oxo, acylalkyl, carboxy esters, carboxyl,
-carboxamido, nitro, acyloxy, aminoalkyl, alkylaminoaryl,
alkylaryl, alkylaminoalkyl, alkoxyaryl, arylamino, arylalkylamino,
alkyl sulfonyl, -carboxamidoalkylaryl, -carboxamidoaryl,
hydroxyalkyl, haloalkyl, alkylaminoalkylcarboxy-,
aminocarboxamidoalkyl-, cyano, alkoxyalkyl, perhaloalkyl,
arylalkyloxyalkyl, and the like.
EXAMPLES AND EMBODIMENTS
[0116] Unless otherwise noted, the reactions described in the
Examples were performed under an oxygen-free atmosphere of argon.
Graduated flasks were used for polymerization reactions with
condensed sulfur dioxide. Anhydrous solvents were obtained using a
solvent purification solvent (Innovative Technologies). All other
chemicals were of reagent grade from Sigma-Aldrich and were used as
received, except for sulfur dioxide, which was purchased from
Airgas, and triphenylbismuthine, which was purchased from Alfa.
Cuprous Bromide was purified as described somewhere else.
Multi-walled carbon nanotubes were donated by Bayer, AG (Baytubes
150 P, >95% purity).
[0117] NMR spectra were obtained on a Bruker Avance (400 MHz). NMR
chemical shifts are given in ppm referenced to CHCl.sub.3/TMS (7.24
ppm for .sup.1H, 77.24 ppm for .sup.13C), unless otherwise noted.
High-resolution mass spectra (HRMS) were obtained on a Bruker
Daltonics APEXII 3 Tesla Fourier Transform Mass Spectrometer at the
MIT Department of Chemistry Instrumentation Facility (DCIF).
Fourier Transform infrared (FT-IR) spectroscopy was performed on a
Perkin-Elmer model 2000 FT-IR spectrophotometer using the Spectrum
v. 2.00 software package. Polymer molecular weights were determined
at room temperature on a HP series 1100 GPC system in THF at 1.0
ml/min (1 mg/mL sample concentrations), approximate molecular
weights were estimated using a polystyrene calibration standard.
Amperometric measurements were performed with an AUTOLAB PGSTAT 20
potentiostat (Eco Chemie) at constant potential (1 V). Gold
electrodes were deposited using a SC7620 Sputter Coater from Quorum
Technologies. The decaying element from the core of a nuclear
reactor was used for the high dose gamma ray source at the gamma
irradiation facility from the nuclear reactor at MIT, and a
Gammacell irradiator Gammacell 40 with a .sup.137Cs source (Model
C-161, Type 8) was used for the lower radiation doses. Optical
Microscopy pictures were obtained using a Leica DMRXP optical
microscope. SEM images were obtained using a JEOL JSM 6060 Scanning
Electron Microscope. Samples for SEM were coated with a Sputterer
with a Au/Pd target to prevent radiation damage.
[0118] Devices were fabricated by drop casting on previously
cleaned microscope slides, using a sonicated THF solution
containing both the POS and the MWCNTs. Films were dried in a
vacuum oven prior to electrochemical measurements. Amperometric
measurements were performed on 6 devices with the same composition
for every data point: 3 of the devices were exposed to radiation,
and 3 of them were not. Each amperometric measurement was performed
three times over 30 s for every device, and averaged before and
after irradiation. The variation in the current intensity produced
was compared between irradiated samples and non-irradiated
samples.
Example 1
##STR00010##
[0120] The following describes a general method for POS synthesis.
A typical Poly (Olefin Sulfone) synthesis was carried out following
literature procedures. In general, sulfur dioxide (6 mL) was
condensed into a graduated vessel at -78.degree. C. The reaction
vessel was then transferred into a -45.degree. C. bath. Olefin
monomers were added to the reaction mixture in the desired ratio,
and the solution was stirred for 5 minutes. Initiator for the
polymerization (tert-Butyl hydroperoxide in decane, solution
5.0-6.0M, 5-10 mol % relative to total amount of olefin) was added,
and the mixture was stirred at -45.degree. C. for 2 h. The
polymerization was stopped by pouring the reaction mixture into
MeOH. The resulting white powder was redissolved in CHCl.sub.3 and
reprecipitated from MeOH, then washed with MeOH. The white solid
obtained was dried under vacuum.
Example 2
##STR00011##
[0122] Poly(1-hexene sulfone) 1 was synthesized using the method
described in Example 1. 98% yield, .delta..sub.H (CDCl.sub.3) 0.9
(3H, br t), 1.3-1.4 (2H, br), 1.4-1.6 (2H, br), 1.8-2.0 (1H, br),
2.0-2.2 (1H, br), 3.2-3.5 (1H, br), 3.7-4.1 (2H, br); .delta..sub.C
(CDCl.sub.3) 13.92. 22.67, 28.12, 28.46, 50.26, 57.34; IR (FIG.
20B, black curve) 2961, 2874, 1309, 1130, 715; GPC M.sub.n=102K,
M.sub.w=367K, D=1.97.
Example 3
##STR00012##
[0124] The following example describes the synthesis of
6-azido-1-hexene. To a solution of 6-bromo-1-hexene (1 ml, 7.5
mmol) in DMSO (20 ml) under argon was added sodium azide (1 g, 15.4
mmol), and the solution was stirred for 42 h at room temperature. A
1:1 mixture of H.sub.2O/diethyl ether was added to the reaction
mixture, and the aqueous phase was extracted three times with 20 mL
Et.sub.2O. The combined organic phases were washed twice with 20 mL
H.sub.2O, 20 ml brine, and dried over MgSO.sub.4. After removal of
the solvent under reduced pressure, a colorless oil was obtained
(652 mg, 69%). .delta..sub.H (CDCl.sub.3) 1.4 (2H, m), 1.6 (2H, m),
2.1 (2H, m), 3.2 (2H, t, J=6.8 Hz), 4.9 (2H, m,), 5.8 (1H, ddt,
6.7, 10.2, 16.9 Hz); .delta..sub.C (CDCl.sub.3) 26.10, 28.44,
33.38, 51.51, 115.19, 138.35.
Example 4
##STR00013##
[0126] Poly(6-azido-1-hexene sulfone) 2 (a/(a+b)=0) was synthesized
using the method described in Example 1. 96% yield; .delta..sub.H
(CDCl.sub.3) 1.5-1.8 (4H, br), 1.8-2.1 (1H, br), 2.1-2.3 (1H, br),
3.3-3.6 (3H, br), 3.7-4.1 (2H, br); .delta..sub.C (CDCl.sub.3)
23.19, 28.18, 28.58, 49.78, 51.00, 57.00; IR (FIG. 20B, bottom
curve) 2942, 2098, 1299, 1234, 1128; GPC M.sub.n=2.9K,
M.sub.w=5.0K, D=1.71.
Example 5
##STR00014##
[0128] Poly(1-hexene 6-azido-1-hexene sulfone), 2 (a/(a+b).noteq.0)
was synthesized using the method described in Example 1.
.delta..sub.H (CDCl.sub.3): mixture of signals at the same
positions as for 1 and 2. X.sub.a, X.sub.b were determined by
comparison of the integration of the signal at 0.9 ppm (3H from
repeat unit a, highlighted in FIG. 20A) and at 1.5-1.8 ppm (4H from
repeat unit b, highlighted in FIG. 20A)). Corresponding IR Spectra
are shown on FIG. 20B. For polymer 2 where X.sub.a=0.56,
X.sub.b=0.44, M.sub.n=4.7K, M.sub.w=9.3K, D=1.99.
Example 6
##STR00015##
[0130] Propargyl pyrenebutyl ether, 3, was synthesized according to
the following method. To a solution of 1-pyrenebutanol (1 g, 3.6
mmol) in anhydrous THF (15 ml) was added NaH (160 mg, 6.7 mmol) at
0.degree. C. The solution was stirred at 0.degree. C. for 30 min,
and propargyl bromide (80% in toluene, 880 mg, 7.4 mmol) was added.
The reaction was stirred at 0.degree. C. in the dark for 30 min,
and then let go to room temperature. After stirring for 15 h, the
reaction was refluxed for 8 h, after which ethyl acetate (10 mL)
and water (10 mL) were added. The aqueous phase was extracted twice
with 10 mL ethyl acetate. The combined organic phases were washed
twice with 15 mL H.sub.2O, and then twice with 15 ml brine, and
dried over MgSO.sub.4. After removal of the solvent under vacuum,
the crude was purified by column chromatography using toluene as
the eluent to give 3 as a pale yellow powder (911 mg, 81%).
.delta..sub.H (CDCl.sub.3) 1.8 (2H, m), 1.9 (2H, m), 2.6 (1H, t,
J=2.4 Hz), 3.4 (2H, t, J=8 Hz), 3.6 (2H, t, J=6.4 Hz), 4.2 (2H, d,
J=2.4 Hz), 7.8-8.3 (9H, m); .delta..sub.C (CDCl.sub.3) 26.19,
29.49, 33.06, 58.00, 69.83, 74.35, 80.15, 123.33, 124.59, 124.71,
124.74, 124.94, 124.96, 125.68, 126.46, 127.07, 127.08, 127.45,
128.50, 129.67, 130.82, 131.34, 135.67; IR 3294, 3040.51, 2933,
2860, 2116, 1102, 844 cm.sup.-1; (HR-MS) found (M+H).sup.+313.1620.
theoretical 313.16.
Example 7
##STR00016##
[0132] The following example describes the synthesis of
(4-ethynylphenyl)diphenylbismuthine, 4. Chlorodiphenylbismuthine
was synthesized from triphenylbismuthine and bismuth trichloride
via a ligand redistribution reaction as described in the
literature. To a solution of (4-bromophenylethynyl)trimethylsilane
(640 mg, 2.5 mmol) in anhydrous THF (26 mL) at -78.degree. C. was
added butyl lithium (1.6 mL solution in THF, 2.6 mmol) and stirred
for 1 h. Chlorodiphenylbismuthine (1 g, 2.5 mmol) dispersed in 13
mL anhydrous THF was added to the reaction mixture, and stirred at
-78.degree. C. for 1.5 h. The reaction was let warm up to room
temperature, and stir for 14 h, after which TBAF (3.8 mL in THF
solution 1.0 M, 3.8 mmol) was added to the reaction mixture. After
4 h of stirring at room temperature, the solvent was removed under
vacuum, and the residue was purified by column chromatography using
hexanes/ethyl acetate 19:1 as the eluent. 4 was obtained as a
colorless oil (685 mg, 59%). .delta..sub.H (THF-d.sup.8) 3.6 (1H,
s), 7.2-7.8 (14H, m); .delta..sub.C (THF-d.sup.8) 79.48, 84.72,
115.38, 122.70, 128.68, 131.44, 134.47, 138.46, 158.59, 158.63 (the
signals for the quaternary carbons directly bound to bismuth are
very weak, as reported in previous compounds); IR 3288, 3058, 2924,
2106, 1570, 1474, 1428, 997, 817, 726, 695, 657, 533, 515, 446
cm.sup.-1; m/z=386 (M.sup.+-C.sub.6H.sub.5), 363
(M.sup.+-C.sub.8H.sub.5), 310 (M.sup.+-2C.sub.6H.sub.5), 286
(M.sup.+-C.sub.6H.sub.5, C.sub.8H.sub.5), 209
(Bi.sup.+=M.sup.+-2C.sub.6H.sub.5, C.sub.8H.sub.5).
Example 8
[0133] The following example describes conditions for the
click-chemistry post-polymerization reaction. On a typical
synthesis of polymer families 5, 6, using standard Schlenk
techniques, the alkynyl coupling partner (1 mmol) was dissolved in
dry DMF (15 mL). Azide-containing POS (1 eq of azide-containing
repeat unit) dissolved in 5 mL of anhydrous DMF was added to the
reaction mixture. CuBr (14.3 mg, 0.1 mmol) and sodium ascorbate
(29.7 mg, 0.15 mmol) dispersed in 5 mL anhydrous DMF were added to
the reaction mixture, then addition of N,N-diisopropylethylamine
(17 .mu.l, 0.1 mmol) followed. The mixture was stirred at room
temperature for 24 h, after which the solvent was removed under
vacuum. The polymer was redissolved in THF, reprecipitated from
MeOH, and washed with copious amounts of saturated aqueous solution
of NH.sub.4Cl. After washing with H.sub.2O, MeOH, the resulting
white solid was dried under vacuum.
Example 9
##STR00017##
[0135] Polymer 5 (24 mol % Pyr) was synthesized according to the
method described in Example 8. Mol % determined by .sup.1H-NMR,
comparing the relative ratio of the broad signal between
.delta..sub.H 7.8-8.2 (9H, pyrene moiety), and 0.9 (3H, methyl
group of hexane repeat unit); M.sub.n=4.9K, M.sub.w=7.2K,
D=1.46.
Example 10
##STR00018##
[0137] Polymer 6 (24 mol % Pyr, 20 mol % Bi) was synthesized
according to the method described in Example 8. M.sub.n=6.7K,
M.sub.w=7.5K, D=1.11.
[0138] FIG. 21 shows IR Spectra of POS with different degrees of
functionalization, including (i) polymer 2 (Example 5), with 44 mol
% of azide-containing repeat unit (X.sub.b=0.44); (ii) polymer 5
(Example 9), with 24 mol % pyrene containing repeat unit, 20 mol %
repeat unit containing azide groups; and (iii) polymer 6 (Example
10), with 24 mol % pyrene containing repeat unit, 20 mol % bismuth
containing repeat unit.
Example 11
[0139] In the following example, devices comprising functionalized
polymers were designed and fabricated. Poly(1-hexene sulfone) 1,
which degrades in the presence of ionizing radiation (e.g., high
energy electrons, gamma rays) and is used as an electron beam
resist, was used as the polymer matrix. In order to achieve good
dispersions of nanotubes (e.g., MWCNTs), good levels of
sensitivity, and improved gamma ray absorption, functional POSs
were synthesized using "click" chemistry. Azide-containing olefins
were synthesized and successfully incorporated into the main chains
of the POSs. As shown in FIG. 3, copolymerization of
6-azido-1-hexene with SO.sub.2 and 1-hexene afforded a family of
random monomodal terpolymers, polymer 2, in which the ratio of
incorporation of olefin to azido-olefin (a/b) was identical to the
feed ratio (A/B) (see FIG. 18, ideal azeotropic copolymerization).
This allowed for substantial control over the loading of azide
functionalities on the side chain of the polymer. Huisgen
1,3-dipolar cycloaddition with alkynyl molecules provided the
desired functionality to our POSs.
[0140] The azide-containing polymers were further functionalized
via click chemistry, using the alkyne-containing species shown in
FIG. 4A. To improve the dispersion capabilities of MWCNTs, pyrene
groups were attached to the side chains of the POSs to increase
pi-pi stacking interactions with the nanostructures (e.g., carbon
nanotubes), while leaving the electronic structure of the
nanostructures intact. Using click-chemistry, pyrene 3 was
incorporated into the POS. (FIG. 4B). This resulted in improved
interaction between MWCNTs and POSs, and consequentially, less
phase separation. As shown in FIG. 4C, stepwise or one-pot
"click-chemistry" reactions of polymer 2 with pyrene derivative 3
and complex 4 yielded polymer families 5 and 6, the latter
incorporating both pyrene and bismuth functionalities. The
resulting polymers, 5 and 6, were characterized by GPC, .sup.1H-NMR
and IR. The presence of Bi in 6 was confirmed by XPS.
[0141] Improved MWCNTs dispersions were created by incorporation of
pyrene into the POS materials utilizing addition reactions to
pendant azides. Microscopy studies revealed improved dispersions
and an increase in the device sensitivity was also observed.
Example 12
[0142] In this example, a device was produced from dispersions of
poly(1-hexene sulfone) and commercially purified MWCNTs. Thin films
of MWCNT/POS were deposited on a microscope slide by drop casting
from a THF solution and gold electrodes were deposited via sputter
coating with a spacing of 1.5 mm between electrodes.
[0143] FIG. 19 shows the increase in conductivity (y axis) of
irradiated devices fabricated using the specified polymer (x axis)
and MWCNTs. (Error bars=standard deviation.) Two radiation doses
were used, 510.sup.6 rad and 510.sup.3 rad. Irradiation of devices
composed of a blend of poly(1-hexene sulfone) 1 with multi-walled
carbon nanotubes (MWCNT) with high doses of gamma radiation
(510.sup.6 rad) yielded an increase in the conductivity of up to
100 fold as compared to a non-irradiated reference of the same
composition.
[0144] To test the dynamic range of the detectors, a lower dose of
510.sup.3 rad was employed, and devices composed of polymer1/MWCNT
also showed a detectable increase in the conductivity as compared
to a non-irradiated reference. However, the conductivity was at the
lower detection limit of our amperometer, and devices did not show
a determinable response when exposed to lower doses. Without
wishing to be bound by theory, the low sensitivity can be
attributed to poor initial dispersion of CNTs in the polymer as
revealed by optical microscopy, and to the low gamma ray
cross-sections of the elements that compose the POS. These problems
can be addressed by using polymers 5 or 6 instead of polymer 1 for
polymer fabrication.
[0145] When devices fabricated using functional POSs 5 and 6 were
exposed to gamma radiation, a more pronounced increase in
conductivity was obtained as compared to devices with the
unfunctionalized equivalent poly(1-hexene sulfone), 1. An increase
in the initial homogeneity of the system also improved the
performance of the devices: if the response of 5 (14 mol % repeat
unit x) and 5 (24 mol % repeat unit x) are compared to the same
dose of radiation (510.sup.3 rad), the signal goes from barely
detectable to an increase of about 14%. Incorporation of Bi to
increase the opacity of the system towards gamma rays proved to be
an even more effective strategy for increasing device response
towards radiation: a 5.12 fold increase in the conductivity was
detected when using polymer 6 for device fabrication.
[0146] Degradation or depolymerization of the POS material was
confirmed by analyzing the molecular weights before and after
radiation exposure by Gel Permeation Chromatography (GPC), and CNT
aggregation could be observed via optical microscopy. FIG. 22 shows
images of films containing (a) multi-walled carbon nanotubes
(MWCNTs), (b) polymer 1/MWCNT, and (c) polymer 5 (24 mol %
Pyrene)/MWCNT. Optical Microscopy (A-C, 40.times., bright field
mode, scale bar 20 .mu.m) and SEM (A1-C1, 23000.times., 15 kV, SEI
detector, no tilt, scale bar 1 .mu.m) images of films composed of
bare MWCNT (A, A1), polymer 1/MWCNT (B, B1), polymer 5 (24 mol %
Pyrene)/MWCNT (C, C1). The optical microscopy pictures reveal how
the degree of aggregation of the MWCNT decreased with increasing
content of pyrene in the side chains of the POS (from FIG. 22B to
FIG. 22 C, clear areas correspond to regions with transparent POS
and MWCNT dispersed in aggregates too small to absorb visible
light). The SEM pictures show that continuous films were formed
when using a POS together with the MWCNT for film deposition.
[0147] FIG. 23 shows images of films containing polymer 1/MWCNT (d)
before irradiation and (e) after irradiation with a high dose of
radiation (Optical Microscopy (D-E, 40.times., bright field mode,
scale bar 20 .mu.m) and SEM (D1-E1, 23000.times., 15 kV, SEI
detector, no tilt, scale bar 1 .mu.m)). The optical microscopy
pictures revealed increases in the degree of aggregation of the
MWCNTs and the formation of pores in the film from gas development.
The SEM pictures show details of the pores formed after
irradiation.
[0148] In summary, a sensing scheme can be deployed for the
detection of uncharged ionization radiation. Functional POSs were
accessed via click-chemistry methods, and several strategies were
successfully deployed for the high sensor sensitivity. Systematic
improvements in sensitivity can be accomplished by rational design,
and incorporation of the appropriate chemical components in a
sensing scheme.
Example 13
[0149] The following example discusses various aspects of high
resolution spectroscopy of gamma rays.
[0150] High-resolution spectroscopic analysis of incident gamma
rays involves differentiation and identification of the energies of
the incoming gamma rays. At an atomic level, ionization by
interaction with gamma rays in materials occurs mainly via three
different phenomena: photoelectric absorption, Compton scattering,
and pair production. In photoelectric absorption, an atom absorbs
the gamma ray, and emits an electron, usually from its K-shell. The
atom, which is left in an excited state, can relax back to the
ground state typically by emitting Auger electrons or x-rays.
Photoelectric absorption dominates in the range of gamma ray
energies up to several hundred keV. By the Compton Effect, a photon
is inelastically scattered by an atomic electron, and part of its
energy is transmitted to the struck electron, leaving it in an
unbound state. The Compton effect dominates for medium-energy gamma
rays. Finally, during pair production, the photon is transformed
into an electron and a positron in the electric field of the
nucleus. The electron formed in this process has high energy, and
produces bremsstrahlung and ionization on its path, while the
positron is annihilated producing new photons. Pair production is
the ionization event that dominates when high-energy gamma-rays are
used (5-10 MeV). The probability of any of these interactions
occurring for a specific gamma ray energy is the cross-section
value for ionization from gamma-ray interaction for that
energy.
[0151] In FIG. 13, the different cross-sections for gamma-ray
interaction for bismuth are shown. At a certain energy, the
cross-section value will have at least two components: the
component for photoelectric absorption of the photon, the component
for Compton scattering, and a third component for pair production
beyond 1.02 MeV, which is the minimum energy required to form an
electron/positron pair. The cross-sections for every element at
certain gamma-ray energies will change with the nature of the
element, and the energy of the incident gamma ray. The total cross
section curve for an element at different values of gamma ray
energies will have a different shape, since the different
components of the total cross section value are related to the
nature of the element with different proportionalities.
[0152] In some embodiments described herein, the electrons produced
upon interaction of the gamma-ray with the polymer matrix can
depolymerize the matrix, and the extent to which this phenomenon
will take place may be directly comparable to the amount of
electrons generated upon ionization. Without wishing to be bound by
theory, this number of electrons typically depends on the amount of
high-Z doping elements incorporated in the matrix, and the chemical
nature of the elements, since different elements have different
cross-sections at different energies. High-resolution spectroscopic
analysis could potentially be achieved by connecting several
devices with varying high-Z elements (complexes or nanostructures
containing Bi, Pb, Tl, Hg . . . ) as shown in FIG. 14.
[0153] For a given device containing a high Z doping element in a
certain ratio, a proportional amount of electrons may be generated
after interaction with gamma rays, and a certain variation in the
amperometric signal (step increase in the current under a certain
voltage) may be generated. This is the "pulse height" of this
device, and the number of times this device gives this pulse height
is its "count" number. Every device with a different amount of
doping element or different doping element may give a different
pulse height, and a different count number. As shown in FIG. 14,
the combination of the pulse heights/counts for the whole series of
devices may give a characteristic spectrum for every incident gamma
ray energy.
[0154] Calibration with monochromatic gamma-ray sources may help
establish the relationship between the shape of the curve pulse
height/counts and the energy of the incident gamma-ray. After this
relationship has been studied, these arrays of devices may be used
for high-resolution spectroscopic analysis and identification of
the unknown energy of an incident gamma ray or the energy
components of a polychromatic incident set of gamma rays.
Example 14
[0155] The following example discusses various aspects of neutron
sensing. The cross section for neutron interaction with materials
may depend on the energy of the incident neutrons. For this reason,
when considering neutron sensing, neutrons are typically classified
depending on their energy: "slow neutrons" are those neutrons that
have energies under 0.5 eV, while "fast neutrons" have energies
above that range. Devices and methods described herein may be
useful in the determination of both slow and fast neutrons.
[0156] "Slow neutron" Detection: One of the most used reactions for
neutron sensing is the .sup.10B(n, .alpha.) reaction, shown in FIG.
15, in which high energy a particles are generated. These .alpha.
particles are highly ionizing along their trajectory. Upon
interaction with the polymer material (e.g., POS) in the devices
described herein, ionization and depolymerization may occur,
leading to a sensing event.
[0157] Boron can be incorporated in the devices by swelling of the
active film with an ionic liquid containing boron. An example of an
ionic liquid suitable for this purpose is
1-butyl-3-methylimidazolium tetrafluoroborate. (FIG. 16) This
liquid incorporates tetrafluoroborate, BF.sub.4.sup.-, very similar
to the motif BF.sub.3, which is commonly used in thermal neutron
gas detectors.
[0158] An alternative for doping for neutron sensing would be the
less commonly used Gadolinium (Gd) metal complexes. .sup.157Gd has
the largest cross section for neutron absorption after .sup.135Xe.
Systems doped with Gd could potentially lead to higher
sensitivities. In an illustrative embodiment, Gd metal complexes
comprising a single or plurality of triple bond moieties may be
incorporated into polymer materials via the click reaction.
[0159] "Fast neutron" Detection: The cross section for neutron
interaction with most materials decreases as the energy of the
incident neutrons increases. A typical strategy in "fast neutron"
detection is the use of moderators as materials that reduce the
energy of the incident neutrons, so that, by the time they reach
the detector, their energies are within the range of detection of
the "slow neutron" detector. Materials commonly used as moderators
are materials with a high content in hydrogen atoms, like paraffin
or polyethylene (PE). Polymer materials described herein may be
used as a moderator, since they also have a high content in
hydrogen atoms. As shown in FIG. 17, a device may include two
moderator layers on either side of a sensor material. In some
cases, the top moderator layer may be a porous POS that would not
only act as a moderator, but could also allow for gas release upon
POS degradation by ionizing radiation.
Example 15
##STR00019##
[0161] A polymer for a sensor material of the present invention was
synthesized according to the scheme described above, wherein a is
1, b is 3, and n is 40. The polymer was then reacted with
GdCl.sub.3 is pyridine at 70.degree. C. for about 2.5 hours to
obtain a composition having the structure:
##STR00020##
wherein the composition may be used in a device or method as
described herein.
[0162] While several embodiments of the present invention have been
described and illustrated herein, those of ordinary skill in the
art will readily envision a variety of other means and/or
structures for performing the functions and/or obtaining the
results and/or one or more of the advantages described herein, and
each of such variations and/or modifications is deemed to be within
the scope of the present invention. More generally, those skilled
in the art will readily appreciate that all parameters, dimensions,
materials, and configurations described herein are meant to be
exemplary and that the actual parameters, dimensions, materials,
and/or configurations will depend upon the specific application or
applications for which the teachings of the present invention
is/are used. Those skilled in the art will recognize, or be able to
ascertain using no more than routine experimentation, many
equivalents to the specific embodiments of the invention described
herein. It is, therefore, to be understood that the foregoing
embodiments are presented by way of example only and that, within
the scope of the appended claims and equivalents thereto, the
invention may be practiced otherwise than as specifically described
and claimed. The present invention is directed to each individual
feature, system, article, material, kit, and/or method described
herein. In addition, any combination of two or more such features,
systems, articles, materials, kits, and/or methods, if such
features, systems, articles, materials, kits, and/or methods are
not mutually inconsistent, is included within the scope of the
present invention.
[0163] The indefinite articles "a" and "an," as used herein in the
specification and in the claims, unless clearly indicated to the
contrary, should be understood to mean "at least one."
[0164] The phrase "and/or," as used herein in the specification and
in the claims, should be understood to mean "either or both" of the
elements so conjoined, i.e., elements that are conjunctively
present in some cases and disjunctively present in other cases.
Other elements may optionally be present other than the elements
specifically identified by the "and/or" clause, whether related or
unrelated to those elements specifically identified unless clearly
indicated to the contrary. Thus, as a non-limiting example, a
reference to "A and/or B," when used in conjunction with open-ended
language such as "comprising" can refer, in one embodiment, to A
without B (optionally including elements other than B); in another
embodiment, to B without A (optionally including elements other
than A); in yet another embodiment, to both A and B (optionally
including other elements); etc.
[0165] As used herein in the specification and in the claims, "or"
should be understood to have the same meaning as "and/or" as
defined above. For example, when separating items in a list, "or"
or "and/or" shall be interpreted as being inclusive, i.e., the
inclusion of at least one, but also including more than one, of a
number or list of elements, and, optionally, additional unlisted
items. Only terms clearly indicated to the contrary, such as "only
one of" or "exactly one of," or, when used in the claims,
"consisting of," will refer to the inclusion of exactly one element
of a number or list of elements. In general, the term "or" as used
herein shall only be interpreted as indicating exclusive
alternatives (i.e. "one or the other but not both") when preceded
by terms of exclusivity, such as "either," "one of," "only one of,"
or "exactly one of." "Consisting essentially of," when used in the
claims, shall have its ordinary meaning as used in the field of
patent law.
[0166] As used herein in the specification and in the claims, the
phrase "at least one," in reference to a list of one or more
elements, should be understood to mean at least one element
selected from any one or more of the elements in the list of
elements, but not necessarily including at least one of each and
every element specifically listed within the list of elements and
not excluding any combinations of elements in the list of elements.
This definition also allows that elements may optionally be present
other than the elements specifically identified within the list of
elements to which the phrase "at least one" refers, whether related
or unrelated to those elements specifically identified. Thus, as a
non-limiting example, "at least one of A and B" (or, equivalently,
"at least one of A or B," or, equivalently "at least one of A
and/or B") can refer, in one embodiment, to at least one,
optionally including more than one, A, with no B present (and
optionally including elements other than B); in another embodiment,
to at least one, optionally including more than one, B, with no A
present (and optionally including elements other than A); in yet
another embodiment, to at least one, optionally including more than
one, A, and at least one, optionally including more than one, B
(and optionally including other elements); etc.
[0167] In the claims, as well as in the specification above, all
transitional phrases such as "comprising," "including," "carrying,"
"having," "containing," "involving," "holding," and the like are to
be understood to be open-ended, i.e., to mean including but not
limited to. Only the transitional phrases "consisting of" and
"consisting essentially of" shall be closed or semi-closed
transitional phrases, respectively, as set forth in the United
States Patent Office Manual of Patent Examining Procedures, Section
2111.03.
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